A cellobiose phosphorylase from Cellvibrio gilvus recognizes only the β-d-form of 5a-carba-glucopyranose
✍ Scribed by Motomitsu Kitaoka; Seiichiro Ogawa; Hajime Taniguchi
- Book ID
- 102993835
- Publisher
- Elsevier Science
- Year
- 1993
- Tongue
- English
- Weight
- 277 KB
- Volume
- 247
- Category
- Article
- ISSN
- 0008-6215
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✦ Synopsis
Cellobiose phosphorylase is an enzyme that catalyzes the reversible phosphorolysis of cellobiose to form a-D-glucose-l-phosphate (G-1-P). The enzyme is present in several microorganisms, such as Clostridium thermocellum', Ruminococcus jlavefaciens2, Cellvibrio gilvus3, Cellulomonas4,5, and Fomes annosus6. The enzyme from Cellvibrio gilvus was the first to be purified to an electrophoretically homogeneous state7. The authors found that its reaction followed an ordered bi-bi mechanism'. Contrary to a previous report'l, Mg2+ is not required for activity. In the reverse reaction, the enzyme can utilize some monosaccharides as the glucosyl acceptor instead of D-glucose'. Its specificity for the acceptor molecule was studied and the results suggested that the enzyme recognized the p-anomeric hydroxyl group of the acceptor p-glucose molecule'. However, the experiment could not clarify whether the enzyme also utilized cY-p-glucose to any extent, because of mutarotation'. The experimental proof using D-glucose is not unequivocal because of the difficulty in estimating the anomeric ratio of o-glucose. Recently, Tsumuraya et a1.l' reported that a maltose phosphorylase reacted with only the cy-pyranose of p-glucose, the reaction was performed at 0°C to minimize the effect of mutarotation. We have chosen a different approach to determine the anomeric specificity on the C. girvus cellobiose phosphorylase.
Diastereoisomers of Sa-carba-aldohexopyranose 6hydroxymethyl-1,2,3,4-cyclohexanetetrol) are carbocyclic analogues of aldohexopyranoses, the ring oxygen atom of which are substituted by a methylene group". If these compounds act as substrate analogues of the respective aldohexopyranoses in the reverse reaction of the cellobiose phosphorylase, results would not be influenced by mutarotation. In