Functional influence of human CYP2D6 allelic variations: P34S, E418K, S486T, and R296C

Article abstract of DOI:10.1007/s12272-013-0212-5

CYP2D6 is responsible for the oxidative metabolism of 20-25 % of clinical drugs and its genetic polymorphisms can significantly influence the drug metabolism. In this study, we analyzed the functional activities of four nonsynonymous single nucleotide polymorphisms from CYP2D652 allele, which were recently found, and one found frequently in CYP2D6 alleles. Recombinant variant enzymes of E418K, S486T, and R296C were successfully expressed in Escherichia coli and purified. However, a CYP holoenzyme spectrum of P34S variant was not detected in E. coli whole cell level. Structural analysis indicated that P34S mutation seemed to perturb a highly conserved proline-rich N-terminus of CYP2D6. Steady state kinetic analyses showed the significant reductions of enzymatic activities in E418K and R296C variants. In the case of bufuralol 1'-hydroxylation, a novel mutant, E418K, showed 32 % decrease in catalytic efficiency (k _cat/K _m) mainly due to the decrease of k _cat value. R296C showed much greater reduction in the catalytic efficiency (9 % of wild-type) due to both of a decrease of k _cat value and an increase of K _m value. In the case of dextromethorphan O-demethylation, E418K showed both of a decrease of k _cat value and an increase K _m value to result in ～43 % reduction of catalytic efficiency. A highly decreased catalytic efficiency (～6 % of wild-type) in the mutant of R296C also was observed mainly due to the dramatic change of k _cat value of dextromethorphan O-demethylation. These results suggested that individuals carrying these allelic variants are likely to have the altered metabolic abilities of many clinical drugs therefore, these polymorphisms of CYP2D6 should be much concerned for reliable drug treatment.

Full text of DOI:10.1007/s12272-013-0212-5

Arch. Pharm. Res.
DOI 10.1007/s12272-013-0212-5
RESEARCH ARTICLE
Functional influence of human CYP2D6 allelic variations: P34S,
E418K, S486T, and R296C
•
Joohwan Kim Young-Ran Lim Songhee Han
•
•
•
Jung-Soo Han Young-Jin Chun Chul-Ho Yun
•
•
•
Chang Hoon Lee Donghak Kim
Received: 4 June 2013 / Accepted: 9 July 2013
Ó The Pharmaceutical Society of Korea 2013
Abstract CYP2D6 is responsible for the oxidative
metabolism of 20–25 % of clinical drugs and its genetic
polymorphisms can significantly influence the drug
metabolism. In this study, we analyzed the functional
activities of four nonsynonymous single nucleotide poly-
morphisms from CYP2D6*52 allele, which were recently
found, and one found frequently in CYP2D6 alleles.
Recombinant variant enzymes of E418K, S486T, and
R296C were successfully expressed in Escherichia coli and
purified. However, a CYP holoenzyme spectrum of P34S
variant was not detected in E. coli whole cell level.
Structural analysis indicated that P34S mutation seemed to
perturb a highly conserved proline-rich N-terminus of
CYP2D6. Steady state kinetic analyses showed the signif-
icant reductions of enzymatic activities in E418K and
R296C variants. In the case of bufuralol 1’-hydroxylation,
a novel mutant, E418K, showed 32 % decrease in catalytic
efficiency (kcat/Km) mainly due to the decrease of kcat
value. R296C showed much greater reduction in the cata-
lytic efficiency (9 % of wild-type) due to both of a decrease
of kcat value and an increase of Km value. In the case of
dextromethorphan O-demethylation, E418K showed both
of a decrease of kcat value and an increase Km value to
result in *43 % reduction of catalytic efficiency. A highly
decreased catalytic efficiency (*6 % of wild-type) in the
mutant of R296C also was observed mainly due to the
dramatic change of kcat value of dextromethorphan
O-demethylation. These results suggested that individuals
carrying these allelic variants are likely to have the altered
metabolic abilities of many clinical drugs therefore, these
polymorphisms of CYP2D6 should be much concerned for
reliable drug treatment.
Keywords P450 ꢀ CYP2D6 ꢀ Allelic variants ꢀ
Polymorphism ꢀ Bufuralol ꢀ Dextromethorphan
Introduction
Human genome contains 57 cytochromes P450 (CYPs,
P450s) enzymes and 15 among them are considered as
xenobiotics metabolic enzymes responsible for the metab-
olism of most of drugs (Stark and Guengerich 2007). Many
adverse drug–drug interactions are attributable to pharma-
cokinetic problems and can be understood in terms of
alterations of CYP-catalyzed reactions (Guengerich 1997).
The genetic polymorphisms of drug metabolizing CYPs is
of particular interest because it can promise the rational
optimization of drug therapy with respect to patient’s
genotype to ensure maximum efficacy with minimal
adverse effects (Lee and Kim 2011).
J. Kim ꢀ Y.-R. Lim ꢀ S. Han ꢀ J.-S. Han ꢀ D. Kim (&)
Department of Biological Sciences, Konkuk University,
120 Neungdong-ro, Gwangjjn-gu, Seoul 143-701, Korea
e-mail: donghak@konkuk.ac.kr
Y.-J. Chun
College of Pharmacy, Chung-Ang University,
Seoul 156-756, Korea
C.-H. Yun
School of Biological Sciences and Technology, Chonnam
National University, Gwangju 500-757, Korea
Genetic polymorphisms in CYP enzymes can cause
dramatic differences in the response to specific drugs and
the debrisoquine poor-metabolizer phenotype of CYP2D6
is a well-known example (Zhou et al. 2004). Clinically, the
C. H. Lee
College of Pharmacy, Dongguk University,
Goyang 410-820, Korea
123

J. Kim et al.
CYP2D6 has been issues due to the large variation in the
genetic polymorphism unlike other CYP enzymes (Lee and
Kim 2011). So far, 105 different human CYP2D6 allelic
variants have been detected and *40 nonsynonymous
single nucleotide polymorphisms (SNPs) have been
reported (http://www.cypalleles.ki.se/) (Lee and Kim
2011). Recently, Lee et al. identified a novel amino acid
change (E418K) of CYP2D6*52 allele from Korean pop-
ulations (Lee et al. 2009). The CYP2D6*52 allele contains
P34S and S486T amino acid changes in addition to E418K
and its frequency was 0.33 % in Korean populations (Lee
et al. 2009). P34S and S486T substitutions were present in
the CYP2D6*10 allele with a very high frequency in Asian
populations (Johansson et al. 1994).
The constructed variant clones were confirmed by nucleo-
tide sequencing analysis.
Expression of recombinant CYP2D6 allelic variants
in E. coli
E. coli strain DH5a was used for transformation of both
pCW(CYP2D6) and pGro12 encoding the chaperone pro-
tein GroEL/ES (Wu et al. 2009). Single transformed col-
onies were selected on LB plate media containing
ampicillin (50 lg/ml) and kanamycin (20 lg/ml) and then
inoculated in 5 ml of LB liquid cultures. After overnight
incubation at 37 °C, 220 rpm, the cultures were transferred
to 500 ml of Terrific broth (TB) containing ampicillin
(50 lg/ml) and kanamycin (20 lg/ml) and incubated at
37 °C, 220 rpm. When the OD600 was reached to approx-
imately 0.5, the induction was done with addition of
1.0 mM isopropyl b-D-thiogalactoside (IPTG), 0.5 mM
5-aminolevulinic acid (ALA), 1.0 mM thiamine, trace
elements, and 0.1 mg/ml arabinose. Cultures were further
incubated for 48 h at 28 °C, 200 rpm, and then harvested
by centrifugation.
In this study, we analyzed the drug metabolic activities
of four mutants (P34S, E418K, P34S/E418K, and S486T)
from a novel CYP2D6*52 allele and one mutant (R296C)
highly found in many CYP2D6 alleles. In view of the
importance of CYP2D6 in the metabolism of many clinical
drugs, we determined the functional outcomes from the
novel mutations of CYP2D6.
Purification of CYP2D6 allelic variant proteins
Materials and methods
The harvested cells were resuspended in TES buffer
(50 mM Tris–acetate, 250 mM sucrose, 0.25 mM EDTA,
pH 7.6) containing lysozyme and incubated for 40 min at
4 °C. Cell pellets were centrifuged and then ultra-sonicated
in 150 ml of sonication buffer containing 10 mM potas-
sium phosphate (pH 7.4), 20 % glycerol (v/v),
6.0 mM Mg-acetate, and 0.1 mM DTT. After ultracentri-
fugation, the membrane fractions were prepared and solu-
bilized in 100 mM Tris–HCl (pH 7.4) buffer containing
20 % glycerol (v/v), 1.0 mM DTT, 0.625 % Na-cholate,
and 1.25 % Triton N-101 (v/v). After ultracentrifugation,
the supernatant containing the solubilized proteins were
loaded into Ni2?-nitrilotriacetate agarose column pre-
equilibrated with 30 mM potassium phosphate buffer (pH
7.4) containing 20 % glycerol (v/v), 5 mM imidazole, and
0.5 M NaCl. After loading, the columns were washed with
30 mM imidazole, and then, eluted with 500 mM imidaz-
ole. The eluted proteins were dialyzed three times in
100 mM potassium phosphate buffer (pH 7.4) containing
20 % glycerol at 4 °C.
Chemicals
Bufuralol, dextromethorphan, dextrorphan, glucose-6-phos-
phate, glucose-6-phosphate dehydrogenase, and NADP?
were purchased from Sigma-Aldrich (St. Louis, MO, USA).
10-Hydroxybufuralol was kindly provided by Professor
F. Peter Guengerich (Vanderbilt University, TN, USA).
Ni2?-nitrilotriacetate agarose was purchased from Qiagen
(Valencia, CA, USA). Other chemicals were of the highest
grade commercially available. Escherichia coli DH5a cells
were purchased from Invitrogen (Carlsbad, CA, USA).
Construction of expression vectors for CYP2D6 allelic
variants
The pCW plasmid containing CYP2D6 gene and 49 His-tag
at C-terminus [pCW(CYP2D6)] was used to construct the
CYP2D6 allelic variants (Hanna et al. 2001). Site-directed
mutagenesis was performed using the QuikChange muta-
genesis kit (Stratagene, La Jolla, CA) with the following
primers: 50-TGCACGCTACTCACCA-30, 50-TGGTGAGT
AGCGTGCA-30 (P34S); 50-TTCCACCCCAAACACTTC-
30, 50-GAAGTGTTTGGGGTGGAA-30 (E418K); 50-TTCC
TGGTGACCCCATCC-30, 50-GGATGGGGTCACCAGGA
A-30 (S486T); 50-GAGAACCTGTGCATAGTG-30, 50-CAC
TATGCACAGGTTCTC-30 (R296C). The P34S/E418K
variant was generated using primers for P34S and E418K.
Catalytic activity analysis
Catalytic activities of CYP2D6 wild type and variant
enzymes in all reactions were determined using the CYP/
NADPH-P450 reductase/phospholipid reconstituted system
(Han et al. 2009, 2012). The reaction mixtures included
50 pmol of purified CYP2D6 enzymes (wild type and
123

Polymorphic variations of CYP2D6
variants), 100 pmol of rat NPR, 30 lg sonicated 1,2-dil-
auroyl-sn-glycero-3-phosphocholine (DLPC), and specified
amount of the substrates in 0.5 ml of 100 mM potassium
phosphate buffer (pH 7.4). An NADPH generating system
(100 mM glucose-6-phosphate, 10 mM NADP?, glucose-
6-phosphate dehydrogenase) was used to initiate the
enzymatic reactions.
bufuralol) and A280 (for dextromethorphan) were moni-
tored respectively. The metabolites were identified using
authentic standards, and the peaks were integrated. Steady
state kinetic parameters were calculated using GraphPad
Prism software (La Jolla, CA, USA).
The reaction metabolites were analyzed using a
reversed-phase ODS column (5 lm, 150 9 4.6 mm, Agi-
lent) equipped with YL9100 HPLC system (Young-Lin,
Korea). For bufuralol 10-hydroxylation, buffer A consisted
of 20 mM Na-ClO4 (pH 2.5) and 10 % CH3CN (v/v), and
buffer B consisted of 20 mM Na-ClO4 (pH 2.5) and 40 %
CH3CN (v/v). The following gradient was used with a flow
rate of 1.0 ml/min: from 0 to 15 min, linear gradient from 0
to 50 % B (v/v); from 15 to 20 min, linear gradient to
100 % B; from 20 to 23 min, held at 100 % B; from 23 to
25 min linear gradient to 100 % A; from 25 to 30 min, held
at 100 % A. For dextromethorphan O-demethylation, the
mobile phase consisted of 20 mM Na-ClO4 (pH 2.5) and
MeOH. The following gradient was used with a flow rate
0.6 ml/min: from 0 to 30 min, linear gradient from 30 to
80 % MeOH; from 30 to 33 min, held at 80 % MeOH;
from 33 to 35 min, linear gradient from 80 to 100 %
MeOH; from 35 to 38 min, held at 100 % MeOH. A242 (for
Results
Expression and purification of recombinant CYP2D6
allelic variant enzymes
All of the five CYP2D6 variants were constructed in the
pCW expression vectors, and recombinant proteins of
CYP2D6 variants were expressed in E. coli DH5a.
Recombinant CYP2D6 expression levels in the whole-cell
cultures were determined by CO-binding spectra (Fig. 1).
The expression level of CYP2D6 wild-type was
*140 nmol/l, and the levels of E418K, S486T, and R296C
were ranged from 40 to 70 nmol/l. However, no CYP
holoenzyme spectrum detected for the P34S and P34S/
E418K variants. This result suggests that the P34S substi-
tution may affect to the accurate folding or expression of
the holoenzyme. Recombinant proteins of CYP2D6 wild-
type and three variants (E418K, S486T, and R296C) were
Fig. 1 Expression of recombinant CYP2D6 allelic variant enzymes in E. coli. CO-binding spectra of CYP enzymes in E. coli whole cells were
measured, and the contents of the CYP holoenzyme were calculated
123

J. Kim et al.
purified using Ni2?-NTA affinity column. The concentra-
tions of all purified CYP2D6 proteins were spectroscopi-
cally determined to 0.5–4.6 lM (data not shown).
and D10,20-bufuralol) (Hanna et al. 2001) (Fig. 2a). In this
study, the enzyme reactions by CYP2D6 and variants showed
10-hydroxybufuralol (retentions time of 6.3 min) was a
major metabolite with co-elution of authentic standards
(Fig. 3a). Minor products were assigned as 6-hydroxybufuralol
(8.4 min), 4-hydroxybufuralol (9.6 min), and D10,20-bufuralol
(11.6 min) based on the previous report (Hanna et al. 2001)
(Fig. 3a).
Bufuralol metabolism by CYP2D6 variants
CYP2D6 converted bufuralol to multiple oxidized products
(10-hydroxybufuralol, 4-hydroxybufuralol, 6-hydroxybufuralol,
Fig. 2 Metabolism of bufuralol and dextromethorphan by CYP2D6. a Oxidation of bufuralol by CYP2D6 (Hanna et al. 2001). b Demethylation
of dextromethorphan by CYP2D6 (Yu and Haining 2001)
123

Polymorphic variations of CYP2D6
15
to both of a decrease of kcat value and an increase of Km
A
value (Fig. 3b; Table 1).
Bufuralol
10
5
1'-OH
Dextromethorphan metabolism by CYP2D6 variants
6-OH
4-OH
Δ1',2'
CYP2D6 catalyzes the O-demethylation reaction of dex-
tromethorphan to produce dextrorphan (Yu and Haining
2001; Lee and Kim 2011) (Fig. 2b). In HPLC analysis, the
metabolic products were observed at 14.3 min (dextror-
phan), and 17.3 min (3-methoxymorphinan), which was
assigned as dextrorphan using an authentic standard and
based on the previous report (Yu and Haining 2001)
(Fig. 4a). Turnover rate of dextromethorphan O-demeth-
ylation by CYP2D6 was relatively slower than bufuralol
10-hydroxylation (Table 1). E418K showed both of a
decrease of kcat value and an increase Km value to result in
*43 % reduction of catalytic efficiency (Table 1; Fig. 4b).
S486T mutant showed a small decrease (*24 %) in the
catalytic efficiency with small increases in both of kcat and
Km values (Table 1; Fig. 4b). A highly decreased catalytic
efficiency (*6 % of wild-type) was observed in the mutant
of R296C mainly due to the dramatic change of kcat value
of dextromethorphan O-demethylation (Table 1; Fig. 4b).
0
-5
0
5
10
15
20
Time (min)
5
4
3
2
1
0
B
Wild-type
E418K
S486T
R296C
0
5
10
15
20
Bufuralol,μM
Fig. 3 Oxidation of bufuralol by CYP2D6. a HPLC chromatograms
of bufuralol oxidation by CYP2D6. 10-OH, 10-hydroxybufuralol;
4-OH, 4-hydroxybufuralol; 6-OH, 6-hydroxybufuralol; D10,2’, D10,
20-bufuralol. The dashed line indicated the control experiment
without NADPH generating system. b Steady-state kinetic analysis
of bufuralol 10-hydroxylation by CYP2D6 allelic variant enzymes.
Each point presented is a mean SD (range) of duplicate assays
Locations of the mutated amino acids in CYP2D6
variants
The X-ray crystal structure of a CYP2D6 (PDB-entry code,
2F9Q) was used to locate the positions of the mutated
residues in the CYP2D6 enzyme (Rowland et al. 2006)
(Fig. 5). The P34S substitution is located in a highly con-
served proline-rich region at N-terminus of CYP2D6
enzyme (Fig. 5). The proline residue in this conserved
region of CYP2D6 seems critical for the stability of protein
and the mutation of this residue is likely to produce a
structurally unstable enzyme. The E418K substitution
seems to be located in K’’-helix region and the S486T is
found in b-4-strands of the fourth sheet region (Fig. 5). We
also found that the R296C substitution is located in
N-terminus of I-helix of CYP2D6 structure (Fig. 5).
Catalytic activities of bufuralol metabolism were deter-
mined by measuring the rates of bufuralol 10-hydroxylation.
Steady-state kinetic parameters were determined for wild-
type and three mutants (Fig. 3b; Table 1). A novel mutant,
E418K, showed 32 % decrease in catalytic efficiency (kcat/
Km) mainly due to the decrease of kcat value (Fig. 3b;
Table 1). S486T mutant exhibited increases in both kcat and
Km values, resulting in no significant change in catalytic
efficiency (Fig. 3b; Table 1). R296C showed much greater
reduction in the catalytic efficiency (9 % of wild-type) due
Table 1 Kinetic parameters of 10-hydroxylation of bufuralol and O-demethylation of dextromethorphan by purified wild-type and variants of
CYP2D6
Mutations
10-Hydroxylation of bufuralol
O-Demethylation of dextromethorphan
kcat (min-1
)
Km (lM)
kcat/Km
kcat (min-1
)
Km (lM)
kcat/Km
WT
3.1 0.3
1.8 0.1
6.1 0.3
0.9 0.1
2.7 1.0
2.3 0.6
5.5 0.8
8.6 1.4
1.14
0.78
1.12
0.10
0.11 0.01
0.08 0.01
0.07 0.01
0.008 0.001
16.1 2.4
21.1 4.4
12.6 1.9
20.2 11.0
0.0068
0.0038
0.0056
0.0004
E418K
S486T
R296C
Results are presented as mean SE
123

J. Kim et al.
10.0
7.5
5.0
2.5
0.0
A
Dm
Dx
MEM
0
5
10
15
20
25
Time (min)
0.10
0.08
0.06
0.04
0.02
0.00
Wild-type
E418K
B
S486T
Fig. 5 Positions of the mutated amino acid residues in CYP2D6. The
positions of the P34S, E418K, S486T, and R296C mutations are
indicated with colors in the ribbon diagram of CYP2D6 X-ray crystal
structure (PDB entry code: 2F9Q). Heme molecule is shown in
orange and the mutated residues in red. (Color figure online)
R296C
0
20
40
60
80
100
CYP2D6 alleles (CYP2D6*10, *14, *36, *47, *49, *54,
*57, and *72) and the significant decreases of their in vivo
activities were consistently reported in other studies (Sak-
uyama et al. 2008; Gaedigk et al. 2006; Matsunaga et al.
2009). Our current study indicates that the loss of functions
in these alleles can be attributed to P34S mutation, there-
fore resulting in the production of non-functional enzyme.
The K’’-helix region, where E418K substitution is loca-
ted, is presumably expected to bind to the reductase partner
(Rowland et al. 2006) (Fig. 5). Therefore, we can speculate
that the substitution of the acidic residue to the basic induces
the perturbation of electron transfer to CYP, therefore
resulting in the decrease of enzymatic activity. The S486T
seems to be located in b-4-strands of the fourth sheet region,
but the change of serine to the alcohol containing threonine
did not affect on the structural or functional basis of
the mutant enzyme (Fig. 5). The R296C substitution in
N-terminus of I-helix of CYP2D6 structure was found in
more than thirty CYP2D6 allelic variants (http://www.
cypalleles.ki.se/). Although many of residues in I-helix
control the substrate specificity, the Arg296 seems not to
interact with substrate directly due to the outward direction
and the alienation from the binding site (Fig. 5). In our
study, the yield of the final purified protein of R296C was
more than five times lower than those of wild-type and the
other mutants (data not shown). This result suggests R296C
mutation may induce the unstable structure of CYP enzyme.
In conclusion, we have expressed four allelic variants
of CYP2D6 and analyzed their catalytic activities.
CYP2D6*52 containing the P34S substitution was
observed to be inactive in the recombinant expression
system that we used, and E418 K and R296C showed the
Dextromethorphan, μM
Fig. 4 Demethylation of dextromethorphan by CYP2D6. a HPLC
chromatograms of dextromethorphan demethylation by CYP2D6.
Dm, dextromethorphan; Dx, dextrorphan; MEM, 3-methoxymorph-
inan. The dashed line indicated the control experiment without
NADPH generating system. b Steady-state kinetic analysis of
O-demethylation of dextromethorphan by CYP2D6 allelic variant
enzymes. Each point presented is a mean SD (range) of duplicate
assays
Discussion
Previously, we studied the expression of CYP2D6 P34S,
E418K, and P34S/E418K variants in COS-7 mammalian
cells using CYP2D6 specific polyclonal antibodies (Lee
et al. 2011). The expression levels of P34S and P34S/
E418K variants showed 4–12 % of wild-type CYP2D6
(Lee et al. 2011). This study indicated that the substitution
of P34S induces the very low level of protein production,
either as a full-length protein or as proteolytic fragments
and this instability of enzyme variant is not due to the
expression system.
In the crystal structure of CYP2D6 (Rowland et al.
2006), the P34S substitution is found in a highly conserved
region encoding the proline-rich N-terminus (Fig. 5).
Structural perturbation of this region seemed to cause
expression of an unstable gene product and reduction of
enzymatic activity as previously proposed by Johansson
et al. (1994). As a result, CYP2D6*52 allele including
P34S mutation is likely to produce an unstable and non-
functional protein regardless of two other substitutions.
This P34S mutation was frequently found in various
123

Polymorphic variations of CYP2D6
Lee, H.J., M.K. Park, Y.R. Park, D. Kim, C.H. Yun, Y.J. Chun, H.J.
Shin, H.S. Na, M.W. Chung, and C.H. Lee. 2011. Expression of
CYP2A6, CYP2D6 and CYP4A11 polymorphisms in COS7
mammalian cell line. Toxicology Research 27: 25–29.
Lee, I.S., and D. Kim. 2011. Polymorphic metabolism by functional
alterations of human cytochrome P450 enzymes. Archives of
Pharmacal Research 34: 1799–1816.
significant contribution of the reduced metabolic activities
of CYP2D6. Due to the importance of CYP2D6 enzyme in
the metabolism of many clinical drugs, the possible effects
of these polymorphisms on the therapeutic efficacy and
toxicity of the drugs should be carefully examined.
Lee, S.J., S.S. Lee, H.J. Jung, H.S. Kim, S.J. Park, C.W. Yeo, and J.G.
Shin. 2009. Discovery of novel functional variants and extensive
evaluation of CYP2D6 genetic polymorphisms in Koreans. Drug
Metabolism and Disposition 37: 1464–1470.
Acknowledgments This work was supported by the National
Research Foundation of Korea (NRF) Grants funded by the Korea
government (MEST) (No. 2011-0016509).
Matsunaga, M., H. Yamazaki, K. Kiyotani, S. Iwano, J. Saruwatari,
K. Nakagawa, A. Soyama, S. Ozawa, J. Sawada, E. Kashiyama,
M. Kinoshita, and T. Kamataki. 2009. Two novel CYP2D6*10
haplotypes as possible causes of a poor metabolic phenotype in
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Rowland, P., F.E. Blaney, M.G. Smyth, J.J. Jones, V.R. Leydon, A.K.
Oxbrow, C.J. Lewis, M.G. Tennant, S. Modi, D.S. Eggleston,
R.J. Chenery, and A.M. Bridges. 2006. Crystal structure of
human cytochrome P450 2D6. Journal of Biological Chemistry
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Sakuyama, K., T. Sasaki, S. Ujiie, K. Obata, M. Mizugaki, M.
Ishikawa, and M. Hiratsuka. 2008. Functional characterization of
17 CYP2D6 allelic variants (CYP2D6.2, 10, 14A-B, 18, 27, 36,
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