Transition glucose-6-phosphate

An interesting phenomenon is presented by the mutases which shift phosphate residues in the metabolism of carbohydrates. They catalyze, for example, the transition glucose 1- phosphate glucose 6-phosphate. In this case, the intermediate glucose 1,6-diphosphate is at the same time coenzyme (i.e. phosphate donor), and the stoichiometrically reacting coenzyme is regenerated from the substrate (cf. Chapt. XV-7, XVII-6). 

T7, Takizawa, T., Yoneyama, Y., Miwa, S and Yoshida, A., A single nucleotide base transition is the basis of the common human glucose-6-phosphate dehydrogenase variant A(+). Genomics 1,228-231 (1987). 

Catalysis may also be observed via transition states or intermediates which are more than six-membered. An example is the hydrolysis of glucose-6-phosphate dianion which surprisingly is more rapid (5 times) than the monoanion. Presumably the relatively acidic 1-hydroxyl group of glucose (p/Ca = 10.8, 100°C) can act as a general-acid catalyst of phosphate group expulsion (58),3 > even though the required chair conformation has all substituents axial, viz. 

Binyamin, Chen and Heller reported that wired enzyme electrodes constituted of glassy carbon electrodes coated with poly(4-vinylpyridine) complexed with [Os(bpy)2Cl] and quarternized with 2-bromoethylamine or poly[(iV-vinylimidazole) complexed with [Os(4,4 -dimethyl-2,2 -bypyridine)2Cl] or poly(vinylpyridine) complexed with [Os(4,4 -dimethoxy-2,2 -bypyridine)2Cl] quaternized with methyl groups lost their electrocatalytic activity more rapidly in serum or saline phosphate buffer (pH 7.2) in the presence of urate and transitional metal ions such as Zn and Fe " " than in plain saline phosphate buffer (pH 7.2). It was reported that as much as two-thirds of the current is lost in 2 h in some anodes. However, when a composite membrane of cellulose acetate, Nafion, and the polyaziridine-cross-linked co-polymer of poly(4-vinyl pyridine) quaternized with bromoacetic acid was applied, the glucose sensor stability in serum was improved and maintained for at least 3 days [27,50]. 

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