Purification and characterization of 1,3-β-D-glucan phosphorylase from Ochromonas danica

Article abstract of DOI:10.1271/bbb.130411

1,3-β-D-Glucan phosphorylase (BGP) is an enzyme that catalyzes the reversible phosphorolysis of 1,3-β- glucosidic linkages to form α-D-glucose 1-phosphate (G1P). Here we report on the purification and characterization of BGP from Ochromonas danica (OdBGP). The purified enzyme preparation showed three bands (113, 118, and 124 kDa) on SDS-polyacrylamide gel electrophoresis. The optimum pH and temperature were 5.5 and 25°C-30°C. OdBGP phosphorolysed laminaritriose, larger laminarioligosaccharides, and laminarin, but not laminaribiose. In the synthesis reaction, laminarin and laminarioligosaccharides served as good acceptors, but OdBGP did not act on glucose. Kinetic analysis indicated that the phosphorolysis reaction of OdBGP follows a sequential Bi Bi mechanism. The equilibrium of the enzymatic reaction indicated that OdBGP favors the reaction in the synthetic direction. Overnight incubation of OdBGP with laminaribiose and G1P resulted in the formation of precipitates, which were probably 1,3-β-glucans.

Full text of DOI:10.1271/bbb.130411

Biosci. Biotechnol. Biochem., 77 (9), 1949–1954, 2013
Purification and Characterization of 1,3-ꢀ-D-Glucan Phosphorylase
from Ochromonas danica
y
Yutaka YAMAMOTO, Daichi KAWASHIMA, Ayu HASHIZUME, Makoto HISAMATSU, and Naoto ISONO
Graduate School of Bioresources, Mie University, Tsu 514-8507, Japan
Received May 22, 2013; Accepted June 25, 2013; Online Publication, September 7, 2013
[doi:10.1271/bbb.130411]
1,3-ꢀ-D-Glucan phosphorylase (BGP) is an enzyme
that catalyzes the reversible phosphorolysis of 1,3-ꢀ-
glucosidic linkages to form ꢁ-D-glucose 1-phosphate
(G1P). Here we report on the purification and charac-
terization of BGP from Ochromonas danica (OdBGP).
The purified enzyme preparation showed three bands
(113, 118, and 124 kDa) on SDS-polyacrylamide gel
electrophoresis. The optimum pH and temperature were
5.5 and 25 ꢀC–30 ꢀC. OdBGP phosphorolysed laminar-
itriose, larger laminarioligosaccharides, and laminarin,
but not laminaribiose. In the synthesis reaction, lami-
narin and laminarioligosaccharides served as good
acceptors, but OdBGP did not act on glucose. Kinetic
analysis indicated that the phosphorolysis reaction of
OdBGP follows a sequential Bi Bi mechanism. The
equilibrium of the enzymatic reaction indicated that
OdBGP favors the reaction in the synthetic direction.
Overnight incubation of OdBGP with laminaribiose and
G1P resulted in the formation of precipitates, which
were probably 1,3-ꢀ-glucans.
investigated the properties of these enzymes in detail.3–7)
Furthermore, Kitaoka et al. have developed a method of
synthesizing a series of laminarioligosaccharides using
these two enzymes.8) Recently, LBPs were found in the
bacteria Paenibacillus sp. and Acholeplasma laidlawii,
and their biochemical properties and amino acid
sequences were reported.9,10)
Similarly to LBP and BOP, BGP is an enzyme
catalyzing the reversible phosphorolysis of 1,3-ꢀ-gluco-
sidic linkages to form G1P. BGP was found in 1969 by
Kauss and Kriebitzsch11) in Poterioochromonas malha-
mensis (previously known as Ochromonas malhamen-
sis), which belongs to the class Synurophyceae. It was
partially purified from a cell-free extract, and its
acceptor specificity was studied in the synthesis reac-
tion. BGP from P. malhamensis acts on side-chain-
branched (1,3;1,6)-ꢀ-glucans (laminarin and chrysola-
minarin), but not on glucose; these properties are
different from those of LBP and BOP, derived from
E. gracilis.4,6) Albrecht and Kauss examined other basic
properties of BGP from P. malhamensis, including
optimum pH, optimum temperature, and kinetic param-
eters,12) but there have been no further detailed charac-
terizations or suggested applications for this enzyme in
the last four decades. Therefore, important character-
istics such as reaction mechanism, molecular mass,
primary structure, and reaction products remain un-
known.
Ochromonas danica belongs to the class Chrysophy-
ceae (golden algae). It is a unicellular freshwater
flagellate that can show both photoautotrophic and
heterotrophic growth. It synthesizes chrysolaminarin as
an intracellular storage polysaccharide.13,14) Although its
genome sequence has not been determined, O. danica is
the only species of Chrysophyceae whose expressed
sequence tags have been reported.15) Here we report the
purification and characterization of BGP from O. danica
(OdBGP). In addition, we found that OdBGP appears to
synthesize 1,3-ꢀ-glucan from G1P and laminaribiose.
Key words: 1,3-ꢀ-D-glucan phosphorylase; Ochromonas
danica; laminarin; laminarioligosacchar-
ides; 1,3-ꢀ-D-glucan
Carbohydrate phosphorylases catalyze the phospho-
rolysis of glycosidic linkages at the nonreducing ends of
oligosaccharides and polysaccharides to form sugar
phosphates.1) Twenty phosphorylases have been identi-
fied, each of which cleaves a specific glycosidic link-
age.2) Because phosphorylase reactions are reversible,
the synthesis reactions of phosphorylases using sugar
phosphates as donor substrates are useful in preparing
oligosaccharides, polysaccharides, and glycosides.1)
Three phosphorylases related to laminarioligosacchar-
ides or 1,3-ꢀ-glucans are known: laminaribiose
phosphorylase (LBP; EC 2.4.1.31), 1,3-ꢀ-oligoglucan
phosphorylase (BOP; EC 2.4.1.30), and 1,3-ꢀ-D-glucan
phosphorylase (BGP; EC 2.4.1.97). LBP and BOP were
found in Euglena gracilis in the 1960s.3,4) Both of
these enzymes catalyze the following reversible reaction:
(1,3-ꢀ-D-glucosyl)n þ Pi $ (1,3-ꢀ-D-glucosyl)nꢀ1 þ ꢁ-
D-glucose 1-phosphate (G1P). However, they have
different substrate preferences. LBP prefers laminari-
biose to larger laminarioligosaccharides, whereas BOP
degrades laminaritriose and larger laminarioligosacchar-
ides faster than laminaribiose.5) Previous studies have
Materials and Methods
Chemicals. Laminaribiose, laminaritriose, laminaritetraose, lami-
naripentaose, laminarihexaose, laminariheptaose, cellobiose, cello-
triose, cellotetraose, and cellopentaose were purchased from Seikagaku
Biobusiness (Tokyo). Laminarin, sophorose, methyl ꢀ-D-glucopyrano-
side, paramylon, and ꢁ-D-glucose 1,6-bisphosphate were from Sigma-
Aldrich (St. Louis, MO). Isomaltose, p-nitrophenyl ꢁ-D-glucopyrano-
y
To whom correspondence should be addressed. Fax: +81-59-231-9684; E-mail: isono@bio.mie-u.ac.jp
Abbreviations: BGP, 1,3-ꢀ-D-glucan phosphorylase; BOP, 1,3-ꢀ-oligoglucan phosphorylase; DP, degree of polymerization; G1P, ꢁ-D-glucose
1-phosphate; LBP, laminaribiose phosphorylase; OdBGP, BGP from Ochromonas danica; PAGE, polyacrylamide gel electrophoresis; TLC, thin-
layer chromatography

1950
Y. YAMAMOTO et al.
side, p-nitrophenyl ꢀ-D-glucopyranoside, and CM-cellulose were from
Nacalai Tesque (Kyoto, Japan). All other chemicals used were from
Wako Pure Chemical Industries (Osaka, Japan), unless otherwise
indicated.
Phosphorolytic activity was measured by quantifying the amount of
G1P by the method described by Michal,21) as follows: The reaction
mixture (50 mL), containing 100 mM sodium acetate buffer (pH 5.5),
50 mM KH2PO4, 1 mM laminaripentaose, and the enzyme, was
incubated at 30 ꢁC for 10 min, unless otherwise indicated. After
boiling for 5 min, an aliquot (20 mL) was mixed with 20 mL of 1 M
Tris–HCl buffer (pH 7.5) containing 10 mM MgCl2, 10 mL of 10 mM
NADPþ, 4 mL of 5 mM ꢁ-D-glucose 1,6-bisphosphate, 4 mL of 5 U/mL
glucose-6-phosphate dehydrogenase (Oriental Yeast, Tokyo), and 2 mL
of 25 U/mL phosphoglucomutase (Oriental Yeast). The mixture was
incubated at 30 ꢁC for 10 min, and then the concentration of G1P was
Algal strain and growth conditions. O. danica NIES-2142 was
obtained from the Microbial Culture Collection at the National
Institute for Environmental Studies (Tsukuba, Japan). O. danica was
precultured at 22 ꢁC for 7 d in 250 mL of O medium containing 1 g/L
of glucose, 1 g/L of polypeptone, 1 g/L of yeast extract, and 0.5 g/L of
beef extract under fluorescent illumination (25 mmol photons/m2/s)
under a 12-h light/dark cycle. This culture was inoculated into 5 L of E
medium containing 15 g/L of glucose, 5 g/L of peptone, and 2 g/L of
yeast extract. After cultivation at 30 ꢁC for 3 d with shaking at 160 rpm
without illumination, the cells were harvested by centrifugation at
6;000 ꢂ g for 10 min and rinsed with distilled water. The cell pellet
was stored at ꢀ30 ꢁC until used.
determined by measuring A340
.
Kinetic analysis. To identify the reaction mechanism and to
determine the kinetic parameters for the phosphorolysis reaction of
OdBGP, initial velocities were measured at various concentrations of
laminaritriose (1, 2, 4, 8, and 10 mM) and KH2PO4 (2, 5, 10, 25, and
40 mM). Kinetic parameters were determined by fitting the data to the
following equation for a sequential Bi Bi mechanism with GraFit 7
software (Erithacus Software, Surrey, UK):
Purification of OdBGP. The cells were suspended in 250 mL of
buffer A (20 mM Tris–HCl, pH 8.0, 1 mM EDTA, and 1 mM dithio-
threitol) plus 1 mM phenylmethylsulfonyl fluoride, and were disrupted
by ultrasonication. After centrifugation at 40;000 ꢂ g at 4 ꢁC for
30 min, the supernatant was fractionated with (NH4)2SO4 from 30% to
70% saturation. The precipitate was dissolved in 50 mL of buffer A.
The solution was dialyzed against buffer A and applied to a column
(16 ꢂ 200 mm) of Q Sepharose FF (GE Healthcare, Buckinghamshire,
UK) equilibrated with the same buffer. The column was washed with
buffer A, and the proteins were eluted with a 600-mL gradient of 0–1 M
NaCl in buffer A. The active fractions were pooled and brought to 30%
saturation with (NH4)2SO4. The solution was applied to a column of
HiTrap Phenyl HP (5 mL, GE Healthcare) equilibrated with buffer A
plus 30% (NH4)2SO4. The column was washed with the same buffer,
and the proteins were eluted with a 250-mL gradient of 30–0%
(NH4)2SO4 in buffer A and, finally, with 50 mL of buffer A. The active
fractions were pooled and dialyzed against buffer B (20 mM Tris–HCl,
pH 7.5, 1 mM EDTA, and 1 mM dithiothreitol). The solution was
applied to a column of RESOURCE Q (1 mL, GE Healthcare)
equilibrated with buffer B. The column was washed with buffer B, and
the proteins were eluted with a 10-mL gradient of 0–190 mM NaCl and
a 200-mL gradient of 190–230 mM NaCl in buffer B. The active
fractions were pooled and stored at 4 ꢁC until used.
v ¼ kcat½E0ꢃ½Aꢃ½Bꢃ=ðKiAKmB þ KmB½Aꢃ þ KmA½Bꢃ þ ½Aꢃ½BꢃÞ
where A is laminaritriose and B is Pi.
Laminarioligosaccharide determination. The concentrations of
laminarioligosaccharides were measured by high-performance liquid
chromatography, as described previously.22)
Product analysis. A reaction mixture containing 50 mM sodium
acetate buffer (pH 5.5), 100 mM G1P, 2.5 mM laminaribiose, 5 mM
dithiothreitol, and 50 mU/mL OdBGP was incubated at 30 ꢁC.
Samples were collected at intervals and boiled for 5 min. They were
analyzed by thin-layer chromatography (TLC) and 1,3-ꢀ-glucan assay,
as described below.
For TLC analysis, the sample (50 mL) was mixed with 50 mg of
Amberlite MB-20 (Sigma-Aldrich, Hþ/CH3COOꢀ form) for 5 min
and centrifuged at 14;000 ꢂ g for 5 min to remove G1P and salts. An
aliquot (10 mL) of the supernatant was concentrated to 1 mL by vacuum
centrifugation and spotted onto a silica gel 60 TLC plate (Merck,
Darmstadt, Germany). The plate was developed twice in AcOEt/
AcOH/H2O (2:2:1, v/v/v), dried, and soaked for 10 s in a solution
containing 5% (v/v) H2SO4 in MeOH. After removal of MeOH by
evaporation, the plate was heated at 100 ꢁC for 10 min to visualize
spots.
Protein analysis. Protein concentrations were determined by
Bradford’s method16) using bovine serum albumin as standard. SDS-
polyacrylamide gel electrophoresis (PAGE) was carried out by the
method of Laemmli17) with a 7.5% polyacrylamide gel, and the gel was
stained with Bio-Safe CBB G-250 stain (Bio-Rad Laboratories,
Hercules, CA). The native molecular mass of OdBGP was determined
by size-exclusion chromatography by HiPrep 16/60 Sephacryl S-300
HR column (GE Healthcare). The column was calibrated with a Gel
Filtration Calibration Kit HMW (GE Healthcare). Native-PAGE was
performed by the method of Davis18) with a 6% polyacrylamide gel,
and the gel was stained with Bio-Safe CBB G-250 stain. Activity
staining was carried out by the method described by Miyatake and
Kitaoka,19) with minor modifications, as follows: After protein
separation by Native-PAGE using a 6% polyacrylamide gel containing
1 mM laminaribiose, the gel was incubated in 100 mM sodium citrate
buffer (pH 4.0) containing 10 mM G1P and 10 mM CaCl2 at 30 ꢁC for
1 h, and then washed with distilled water. The gel was soaked in 70 mM
Tris–HCl buffer (pH 7.2) containing 3 mM Pb(NO3)2 for 1 h, washed
with distilled water, and stained with 5% (NH4)2S.
1,3-ꢀ-Glucan assay was performed by the method described by
Shedletzky et al.,23) with minor modifications. The sample (50 mL) was
mixed with 10 mL of 6 M NaOH and kept at 80 ꢁC for 30 min. After the
addition of 210 mL of the aniline blue mix,23) the mixture was
incubated at 50 ꢁC for 30 min and then at room temperature for 30 min.
The fluorescence intensity (excitation, 360 nm; emission, 530 nm) of
the mixture was measured with a fluorescence multi-well plate reader,
CytoFluor II (PerSeptive Biosystems, Framingham, MA).
Results and Discussion
Purification of OdBGP
OdBGP was purified from a cell-free extract of
O. danica NIES-2142 by ammonium sulfate fractiona-
tion and 3 steps of column chromatography (Table 1).
The overall purification was 93.3-fold with a yield of
16.7%, and the specific activity (measured in the
synthetic direction) of the purified OdBGP was
26.5 U/mg. Approximately 2 mg of purified OdBGP
was obtained from 5 L of culture.
The purified enzyme preparation showed three bands
on SDS–PAGE, with molecular masses of 113, 118, and
124 kDa (Fig. 1A). These polypeptides could not be
separated by further chromatography. Extraction and
purification in the presence of various protease inhibitors
also gave the same band pattern (data not shown),
Enzyme assays. Synthetic activity was measured by quantifying the
amount of Pi by the method described by Saheki et al.,20) as follows:
The reaction mixture (100 mL), containing 100 mM sodium citrate
buffer (pH 5.5), 10 mM G1P, 1 mM laminaripentaose, and the enzyme,
was incubated at 30 ꢁC for 10 min, unless otherwise indicated. The
reaction was terminated by adding 1 mL of molybdate reagent (15 mM
ammonium molybdate and 100 mM zinc acetate, pH 5.0) and 250 mL of
10% ascorbic acid reagent (pH 5.0). The mixture was incubated at
30 ꢁC for 15 min, and then the concentration of Pi was determined by
measuring A850. One unit (U) of enzyme activity was defined as the
amount of enzyme that produces 1 mmol of Pi per min.

1,3-ꢀ-D-Glucan Phosphorylase from Ochromonas danica
Table 1. Summary of the Purification of OdBGP
1951
A
B
Total
activity protein activity
Total
Specific
Purifi-
cation
(-fold)
Yield
(%)
100
80
60
40
20
0
100
80
60
40
20
0
Procedure
(U)
(mg)
(U/mg)
Crude extract
(NH4)2SO4
(30–70%)
349
241
1,230
348
0.284 100
0.693
1
2.44
69.1
Q Sepharose FF
HiTrap Phenyl HP
RESOURCE Q
159
45.0
3.53
9.85
45.6 12.4
22.6 34.7
16.7 93.3
78.8
58.4
8.00
2.20 26.5
2
3
4
5
6
7
8
9 10
3
4
5
6
7
8
9 10
pH
pH
A
(kDa)
B
C
Fig. 2. Effects of pH on OdBGP Activity.
1
2
3
4
(A) Optimum pH. The synthetic activity of OdBGP was measured
at 30 ꢁC for 10 min in 100 mM buffer at various pH values (hollow
circle, sodium citrate; solid circle, 3-morpholinopropanesulfonic
acid-NaOH; hollow triangle, Tris–HCl; solid triangle, glycine-
NaOH). (B) pH Stability. The enzyme was incubated at 4 ꢁC for 15 h
in 100 mM buffer at various pH values (hollow circle, sodium citrate;
solid circle, 3-morpholinopropanesulfonic acid-NaOH; hollow tri-
angle, Tris–HCl; solid triangle, glycine-NaOH), and then residual
synthetic activity was measured.
200
116
97
66
45
A
B
100
80
60
40
20
0
100
80
60
40
20
0
Fig. 1. Gel Electrophoresis of Purified OdBGP.
The purified enzyme preparation was analyzed by SDS–PAGE
(A), native-PAGE (B), and activity staining (C). Lane 1, molecular
mass markers; lanes 2–4, purified OdBGP.
suggesting that the multiple bands were probably not
due to a proteolytic artifact. The native molecular mass
of the purified enzyme was estimated to be approx-
imately 250 kDa by size-exclusion chromatography,
indicating that OdBGP is a homodimer and/or a
heterodimer. Because a broad band, which may be a
set of closely overlapping bands, was observed on
native-PAGE (Fig. 1B), the dimeric protein species
were thought to be structurally similar. Activity staining
after native-PAGE indicated that the band(s) had
OdBGP activity in the synthetic direction (Fig. 1C).
The molecular masses of the polypeptides in the
preparation of purified OdBGP were similar to those
of LBPs from E. gracilis (120 kDa)7) and Paenibacillus
sp. (100 kDa).9) Moreover, both LBPs were found to be
dimeric. Structural analysis of OdBGP is currently in
progress.
10 20 30 40 50 60 70
10 20 30 40 50 60
Temperature (°C)
Temperature (°C)
Fig. 3. Effects of Temperature on OdBGP Activity.
(A) Optimum temperature. The synthetic activity of OdBGP was
measured at various temperatures for 10 min in 100 mM sodium
citrate buffer (pH 5.5). (B) Thermal stability. The enzyme was
incubated at various temperatures for 30 min in 20 mM Tris–HCl
buffer (pH 7.5), and then residual synthetic activity was measured.
were almost the same as those on synthetic activity (data
not shown).
Substrate specificity
The phosphorolytic activity of OdBGP toward various
substrates was examined (Table 2). Kauss and Krie-
bitzsch have reported that BGP from P. malhamensis
catalyzes the phosphorolysis of laminarin, but they did
not examine the phosphorolytic activity of this enzyme
toward other substrates.11) In addition to laminarin,
laminaritriose and the larger laminarioligosaccharides
were degraded by OdBGP. The activity toward lami-
naripentaose and laminarihexaose was particularly high.
On the other hand, we found that OdBGP showed no
phosphorolytic activity toward laminaribiose, which is
the best substrate for LBPs5,7,9,10) and a good substrate
for BOP.5) Furthermore, OdBGP did not catalyze the
phosphorolysis of the other glucobioses, glucosides, or
cellooligosaccharides listed in Table 2.
Effects of pH and temperature
The effects of pH and temperature on OdBGP activity
and stability were examined by assaying synthetic
activity. The optimum pH for OdBGP was approxi-
mately 5.5 (Fig. 2A), similar to that of BGP from
P. malhamensis (pH 5.5)12) but lower than those pre-
viously reported for LBPs (pH 6.0–7.2)7,9,10,24) and BOP
(pH 7.0–7.5).4) The activity of OdBGP was low at
neutral pH, and almost no activity was observed at
pH 8.5. The enzyme was stable between pH 4.7 and 9.1
at 4 ꢁC for 15 h (Fig. 2B). The optimum temperature for
OdBGP was 25 ꢁC–30 ꢁC (Fig. 3A), higher than that of
BGP from P. malhamensis (22.5 ꢁC).12) OdBGP was
stable at up to 40 ꢁC at pH 7.5 for 30 min (Fig. 3B). The
effects of pH and temperature on phosphorolytic activity
The acceptor specificity of OdBGP in the synthesis
reaction was also investigated (Table 2). Previous
studies have indicated that laminarin is a good acceptor
for BGP from P. malhamensis,11) whereas it did not

1952
Y. YAMAMOTO et al.
Table 2. Relative Activity of OdBGP toward Various Substrates
0.1
0.08
0.06
0.04
0.02
0
Relative activity (%)b
a
Substrate (1 mM )
Phosphorolysis Synthesis
Glucose
Laminaribiose
Laminaritriose
0
0
0
69
81
99
100
95
359
3
70
73
100
94
89
0
Laminaritetraose
Laminaripentaose
Laminarihexaose
Laminarin
-0.2
0
0.2 0.4 0.6 0.8
1
Cellobiose
Cellotriose
-1
1/Laminaritriose (mM )
0
6
Cellotetraose
Cellopentaose
0
9
Fig. 4. Double-Reciprocal Plot of the Phosphorolysis of Laminari-
triose.
The concentrations of Pi were as follows: hollow circle, 2 mM;
solid circle, 5 mM; hollow triangle, 10 mM; solid triangle, 25 mM;
hollow square, 40 mM.
0
13
2
Sophorose
Gentiobiose
0
0
0
Trehalose
Kojibiose
0
0
0
0
Nigerose
Maltose
Isomaltose
0
0
0
0
A
B
0
0
Methyl ꢁ-D-glucopyranoside
Methyl ꢀ-D-glucopyranoside
p-Nitrophenyl ꢁ-D-glucopyranoside
p-Nitrophenyl ꢀ-D-glucopyranoside
0
0
0
1
10
8
10
8
0
0
56
0
6
6
aBut 10 mg/mL for laminarin.
bActivity toward laminaripentaose was taken to be 100%.
4
4
2
2
serve as an acceptor for LBP6) or BOP4) from E. gra-
cilis. Similarly to P. malhamensis BGP, OdBGP showed
high activity with laminarin as acceptor in the synthesis
reaction. Furthermore, we found that various laminar-
ioligosaccharides also functioned as acceptor substrates,
though this was not examined in a previous study of
BGP isolated from P. malhamensis.11) OdBGP showed
high activity toward laminaritetraose, laminaripentaose,
and laminarihexaose. Similarly to BGP from P. malha-
mensis,11) OdBGP did not act on glucose, which is a
good acceptor for LBPs and BOP.5,7,9,10) Thus, the
substrate specificity of OdBGP toward laminarioligo-
saccharides and glucose in the synthesis reaction was
compatible with that in the phosphorolysis reaction.
Slight activity was observed toward cellobiose and
sophorose, but gentiobiose did not serve as an acceptor.
Moreover, OdBGP showed low activity toward cello-
triose and the larger cellooligosaccharides. The ꢁ-linked
glucobioses and glucosides listed in Table 2 did not
function as acceptor substrates. In contrast to some
LBPs6,7,9,24) and BOP,4) OdBGP was virtually inactive
toward methyl ꢀ-D-glucopyranoside, but OdBGP
showed high activity toward p-nitrophenyl ꢀ-D-gluco-
pyranoside. Thus, we confirmed that the substrate
specificity of OdBGP is distinctly different from those
of LBPs and BOP.
0
0
0
1
2
3
0
1
2
3
Time (h)
Time (h)
Fig. 5. Changes in the Concentrations of Pi and G1P during the
Enzymatic Reaction.
OdBGP (50 mU/mL) was incubated at 30 ꢁC in 100 mM sodium
acetate buffer (pH 5.5) with substrates. Samples were collected at
intervals and boiled for 5 min. The concentrations of Pi (hollow
symbols) and G1P (solid symbols) in the samples were then
determined. The substrates in the reaction mixture at the start of the
reaction were as follows: (A) circles, 10 mM laminaritriose and
10 mM Pi; triangles, 10 mM laminaripentaose and 10 mM Pi; squares,
20 mg/mL laminarin and 10 mM Pi; (B) circles, 10 mM laminari-
triose and 10 mM G1P; triangles, 10 mM laminaripentaose and 10 mM
G1P; squares, 20 mg/mL laminarin and 10 mM G1P.
parameters obtained were as follows: kcat ¼ 400 sꢀ1
,
KmA ¼ 4:1 mM, KmB ¼ 4:4 mM, KiA ¼ 16 mM (A, lami-
naritriose; B, Pi).
Equilibrium of the enzymatic reaction
OdBGP can catalyze reactions in both synthetic and
phosphorolytic directions, as described above. To study
the equilibrium of the OdBGP reaction, changes in the
concentrations of Pi and G1P during incubation of
OdBGP (50 mU/mL) at pH 5.5 and 30 ꢁC were meas-
ured. When 10 mM Pi and 10 mM laminaritriose were
used as substrates, only 0.7 mM G1P was formed after
1 h of reaction (Fig. 5A). A longer incubation period did
not increase the amount of G1P, indicating that the
reaction reached equilibrium. On the other hand, when
10 mM G1P and 10 mM laminaritriose were used as
substrates, the concentration of G1P fell to 2.2 mM after
30 min of reaction, and then it decreased to a steady
value of 1.0 mM after 1 h (Fig. 5B). In both experiments,
the sum of G1P and Pi was constant at 10 mM throughout
the reaction. Furthermore, similar changes in Pi and G1P
concentrations were observed when 10 mM laminaripen-
Kinetic analysis
Double reciprocal plots of the initial velocity of
OdBGP against the laminaritriose concentration at
several concentrations of Pi showed a series of straight
lines intersecting at a point (Fig. 4), which indicates that
the phosphorolysis reaction of OdBGP follows a
sequential Bi Bi mechanism, consistently with the
reactions of other phosphorylases that act on ꢀ-linked
glucooligosaccharides, including LBPs7,9,10) and cello-
biose phosphorylases (EC 2.4.1.20).25–29) The kinetic

1,3-ꢀ-D-Glucan Phosphorylase from Ochromonas danica
1953
taose or 20 mg/mL of laminarin was used as substrate
instead of 10 mM laminaritriose (Fig. 5). Thus, under
these experimental conditions, the amount of G1P was
much smaller than that of Pi at the equilibrium state.
Equilibrium constants were calculated for the following
reactions:
G1
L2
L3
L4
Laminaritriose þ Pi $ Laminaribiose þ G1P
Laminaritetraose þ Pi $ Laminaritriose þ G1P
ð1Þ
ð2Þ
L5
L6
L7
Laminaripentaose þ Pi $ Laminaritetraose þ G1P ð3Þ
Laminarihexaose þ Pi $ Laminaripentaose þ G1P ð4Þ
M
0
0.33 0.66
1
2
4
8
16
The constants (K1, K2, K3, and K4) were 0.13, 0.11, 0.11,
and 0.17, respectively. These results indicate that
OdBGP favors the reaction in the synthetic direction.
This is similar to the properties of other phosphorylases
related to ꢀ-linked glucooligosaccharides, including
LBPs,6,24) BOP,4) cellobiose phosphorylases,25,26,30) and
cellodextrin phosphorylase (EC 2.4.1.49).31)
Reaction time (h)
Fig. 6. TLC Analysis of the Products Synthesized by OdBGP.
OdBGP (50 mU/mL) was incubated at 30 ꢁC in 50 mM sodium
acetate buffer (pH 5.5) with 100 mM G1P and 2.5 mM laminaribiose.
Samples were collected at intervals and boiled for 5 min. Then they
were desalted, concentrated, and analyzed by TLC. M, marker; G1,
glucose; L2, laminaribiose; L3, laminaritriose; L4, laminaritetraose;
L5, laminaripentaose; L6, laminarihexaose; L7, laminariheptaose.
Previous reports have stated that LBP and BOP from
E. gracilis5,6) and BGP from P. malhamensis11) might be
involved in the degradation of intracellular 1,3-ꢀ-glucan
(paramylon or chrysolaminarin), although no evidence
was presented, but it is difficult to determine the
physiological role of phosphorylases. For example, plant
starch phosphorylase (EC 2.4.1.1) catalyzes the rever-
sible phosphorolysis of 1,4-ꢁ-glucan, and it has been
suggested that it functions mainly in the mobilization of
starch in view of its low affinity to G1P and the
relatively high Pi/G1P ratio in plant cells,32) but recent
studies indicate that starch phosphorylase from rice
endosperm strongly favors synthesis over the degrada-
tion of 1,4-ꢁ-glucan even under conditions of excess Pi,
and that it plays a crucial role in starch biosynthesis in
vivo.33,34) Further studies are necessary to assess the
physiological function of OdBGP.
0 h
1 h
2 h
Enzymatic
4 h
products
8 h
16 h
24 h
Laminaribiose
Laminariheptaose
Curdlan
Paramylon
CM-cellulose
None
0
250 500 750 1000 1250
Fluorescence (RFU)
Fig. 7. 1,3-ꢀ-Glucan Assay of the Products Synthesized by OdBGP.
OdBGP (50 mU/mL) was incubated at 30 ꢁC in 50 mM sodium
acetate buffer (pH 5.5) with 100 mM G1P and 2.5 mM laminaribiose.
Samples were collected at intervals and boiled for 5 min. Enzymatic
products (or 10 mg/mL of commercial carbohydrates for compar-
ison) were stained with aniline blue, and the fluorescence intensity
was measured.
Product analysis
As mentioned above, OdBGP catalyzes the reversible
phosphorolysis of 1,3-ꢀ-glucosidic linkages and favors
the reaction in the synthetic direction. In addition, it uses
laminarioligosaccharides of various sizes and laminarin
as acceptors in the synthesis reaction. On the basis of
these findings, we expected that OdBGP would produce
large laminarioligosaccharides or 1,3-ꢀ-glucans by
oligomerization or polymerization of glucose when we
used a large amount of G1P and small amounts of low
molecular mass laminarioligosaccharides as starting
materials. To confirm this, OdBGP was incubated with
2.5 mM laminaribiose and 100 mM G1P for various
periods (the longest being overnight), after which the
reaction products were analyzed.
After removing G1P and other salts by means of ion-
exchange resins, the products were analyzed by TLC
(Fig. 6). During the first 1 h of the reaction, several spots
thought to be a series of small laminarioligosaccharides
were observed. A spot at the origin of the TLC plate
appeared after 2 h, indicating that high molecular mass
products had formed. Spots corresponding to laminar-
ibiose (the initial substrate) and small laminarioligosac-
charides (e.g., laminaritriose and laminaritetraose) al-
most disappeared after 4 h. After more than 8 h, only a
single spot was observed at the origin. Thus, incubation
of OdBGP with laminaribiose and G1P under these
experimental conditions resulted in the formation of
various laminarioligosaccharides and larger products.
The short-term products contained only small laminar-
ioligosaccharides and not high molecular mass products,
which suggests that OdBGP elongates laminarioligosac-
charides or 1,3-ꢀ-glucans distributively (non-proces-
sively) rather than processively.
The products were also analyzed by 1,3-ꢀ-glucan
assay with aniline blue dye. It is well known that 1,3-ꢀ-
glucan forms a fluorescent complex upon interaction
with a fluorochrome present in this dye.35) The fluo-
rescence intensity of the samples during the first 8 h of
reaction was low, comparable to the background
(Fig. 7). In contrast, the intensity increased several fold
after an overnight reaction, indicating that 1,3-ꢀ-glucan
was synthesized.
Overnight incubation of OdBGP with these substrates
resulted in the formation of precipitates (data not
shown). Ogawa et al. prepared laminarioligosaccharides
and 1,3-ꢀ-glucans with a degree of polymerization (DP)
of 10–170 by formic acid hydrolysis of curdlan, a gel-

1954
Y. YAMAMOTO et al.
forming linear 1,3-ꢀ-glucan of DP > 200.36) They
reported that 1,3-ꢀ-glucans with DP 30–170 were
insoluble in water, whereas laminarioligosaccharides
with DP < 20 were soluble. Therefore, it appears that
the products formed after overnight incubation were 1,3-
ꢀ-glucans of DP > 30. The characteristics of the
enzymatic products, including structure, molecular
mass, and morphology, will be reported elsewhere in
detail.
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