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Key Word Index - Sargassum muticum; Fucales; sorbitol; mannitol; guluronic acid; alginic acid; epimerase; biosynthesis.Radioactive D-sorbitol 6-phosphate injected into young growing Sargassum muticum tips is transformed within a few hours into radioactive L-guluronic acid.A C5-epimerase intervenes reversibly to balance the ratio of mannuronic and guluronic acids in the newly synthesized alginic acid.

1-Deoxy-D-sorbitol, the 1-deoxy analogue of D-sorbitol, has been detected in human urine as well as in natural herbs and spices. Although there are sporadic reports about 1-deoxy-D-sorbitol dehydrogenase, the complete catabolic pathway of 1-deoxy-D-sorbitol remains unsolved. Informed by the promiscuous activities of fructose-6-phosphate aldolase (FSA) which is involved in the sorbitol (glucitol) utilization (gut) operon and guided by the large scale bioinformatics analysis, we predicted and then experimentally verified the gut operon encoded by Bacillus licheniformis ATCC14580 is responsible for the catabolism of both D-sorbitol and 1-deoxy-D-sorbitol by in vitro activity assays of pathway enzymes, in vivo growth phenotypes, and transcriptomic studies. Moreover, the phylogenetic distribution analysis suggests that the D-sorbitol and 1-deoxy-D-sorbitol catabolic gene cluster is mostly conserved in members of Firmicutes phylum.

NtdC is an NAD-dependent dehydrogenase that catalyzes the conversion of glucose 6-phosphate (G6P) to 3-oxo-glucose 6-phosphate (3oG6P), the first step in kanosamine biosynthesis in Bacillus subtilis and other closely-related bacteria. The NtdC-catalyzed r

A long-chain mannitol-1-phosphate dehydrogenase (MPD) was characterized for the first time from fungal entomopathogen Beauveria bassiana by gene cloning, heterogeneous expression and activity analysis. The cloned gene BbMPD consisted of a 1334-bp open reading frame (ORF) with a 158-bp intron and the 935-bp upstream and 780-bp downstream regions. The ORF-encoded 391-aa protein (42 kDa) showed less than 75% sequence identity to 17 fungal MPDs documented and shared two conserved domains with the fungal MPD family at the N- and C-terminus, respectively. The new enzyme was expressed well in the Luria-Bertani culture of engineered Escherichia coli BL21 by 16-h induction of 0.5 mM isopropyl 1-thio-β-d-galactopyranoside at 20 °C after 5-h growth at 37 °C. The purified BbMPD exhibited a high catalytic efficiency (kcat/Km) of 1.31 × 104 mM-1 s-1 in the reduction of the highly specific substrate d-fructose-6-phosphate to d-mannitol-1-phosphate. Its activity was maximal at the reaction regime of 37 °C and pH 7.0 and was much more sensitive to Cu2+ and Zn2+ than to Li+ and Mn2+. The results indicate a crucial role of BbMPD in the mannitol biosynthesis of B. bassiana.

Aldose-6-phosphate reductase (A6PRase) is a key enzyme for glucitol biosynthesis in plants from the Rosaceae family. To gain on molecular tools for enzymological studies, we developed an accurate system for the heterologous expression of A6PRase from apple leaves. The recombinant enzyme was expressed with a His-tag alternatively placed in the N- or C-terminus, thus allowing the one-step protein purification by immobilized metal affinity chromatography. Both, the N- and the C-term tagged enzymes exhibited similar affinity toward substrates, although the kcat of the latter enzyme was 80-fold lower than that having the His-tag in the N-term. Gel filtration chromatography showed different oligomeric structures arranged by the N- (dimer) and the C-term (monomer) tagged enzymes. These results, reinforced by homology modeling studies, point out the relevance of the C-term domain in the structure of A6PRase to conform an enzyme having optimal specific activity and the proper quaternary structure.

A putative long-chain mannitol-1-phosphate 5-dehydrogenase from Aspergillus fumigatus (AfM1PDH) was overexpressed in Escherichia coli to a level of about 50% of total intracellular protein. The purified recombinant protein was a ≈40-kDa monomer in solution and displayed the predicted enzymatic function, catalyzing NAD(H)-dependent interconversion of d-mannitol 1-phosphate and d-fructose 6-phosphate with a specific reductase activity of 170 U/mg at pH 7.1 and 25 °C. NADP(H) showed a marginal activity. Hydrogen transfer from formate to d-fructose 6-phosphate, mediated by NAD(H) and catalyzed by a coupled enzyme system of purified Candida boidinii formate dehydrogenase and AfM1PDH, was used for the preparative synthesis of d-mannitol 1-phosphate or, by applying an analogous procedure using deuterio formate, the 5-[2H] derivative thereof. Following the precipitation of d-mannitol 1-phosphate as barium salt, pure product (>95% by HPLC and NMR) was obtained in isolated yields of about 90%, based on 200 mM of d-fructose 6-phosphate employed in the reaction. In situ proton NMR studies of enzymatic oxidation of d-5-[2H]-mannitol 1-phosphate demonstrated that AfM1PDH was stereospecific for transferring the deuterium to NAD+, producing (4S)-[2H]-NADH. Comparison of maximum initial rates for NAD+-dependent oxidation of protio and deuterio forms of d-mannitol 1-phosphate at pH 7.1 and 25 °C revealed a primary kinetic isotope effect of 2.9 ± 0.2, suggesting that the hydride transfer was strongly rate-determining for the overall enzymatic reaction under these conditions.

Bacterial non-specific acid phosphatases normally catalyze the dephosphorylation of a variety of substrates. As shown previously the enzymes from Shigella flexneri and Salmonella enterica are also able to catalyze the phosphorylation of inosine to inosine monophosphate and D-glucose to D-glucose 6-phosphate (D-G6P) using cheap pyrophosphate as the phosphate donor. After optimization high yields (95%) are achieved in the latter reaction and we show here that it is possible to use these enzymes in a preparative manner. This prompted us to investigate by using 31P NMR and HPLC also the phosphorylation of a broad range of carbohydrates and alcohols. Many cyclic carbohydrates are phosphorylated in a regioselective manner. Non-cyclic carbohydrates are phosphorylated as well. Phosphorylation of linear alcohols, cyclic and aromatic alcohols is also possible. In all cases the acid phosphatase from Shigella prefers a primary alcohol function above a secondary one. We conclude that these enzymes are an attractive alternative to existing chemical and enzymatic methods in the phosphorylation of a broad range of compounds.

The design and two synthetic pathways to aminophosphonate 4 which mimics the ionic and steric properties of putative oxocarbenium intermediate 3 in the Kdo8P synthase-catalyzed reaction are reported. It was found that 4 is a slow-binding, most potent inhibitor of the enzyme yet tested, with a K(i) value of 0.4 μM. Copyright (C) 1999 Elsevier Science Ltd.

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