Glucose diphosphate

Leloir110(a) has described a conversion of D-mannosyl phosphate to D-mannose 6-phosphate by phosphoglucomutase, and here, too, the reaction requires catalytic quantities of a-D-glucose 1,6-diphosphate. The role of the latter is probably to generate a-D-mannose 1,6-diphosphate as follows. 

Phosphoglucomutase acts not only on D-glucose and D-mannose phosphates (see p. 204) but also on D-ribose phosphates, the interconversion of D-ribosyl phosphate and D-ribose 5-phosphate being similarly accelerated by D-glucose 1,6-diphosphate,193 which appears to generate D-ribose 1,5-diphos-phate as cofactor.199(a) (b) (o) D-Ribose 5-phosphate is formed from D-ribose and ATP in the presence of yeast ribokinase.m... 

D-glucosamine 6-phosphate to D-glucosamine 1-phosphate. a-D-Glucose 1,6-diphosphate is a cofactor, 264(e)... 

Phosphoglucomutase (EC 2.7 5.l) slowly converts R-l-P to ribose-5-phosphate. A mixture of 35 mM R-l-f O J-P, 17mM R-l-[ L 0l(]-P and less than lmg glucose-1,6-diphosphate at pH 7 33 was equilibrated with phosphoglucomutase (Sigma, P3397, rabbit muscle), at 25°C for 3 Hr. The 31p NMR spectrum was recorded at pH 7 37- The enzyme converted ca. 20 to a mixture of ribose-5-phosphate l Ol (resonance identified by addition of authentic material) and I80I803 species. This demonstrated that the enzyme catalyzed formation of the 0-P bond. 

Phosphoglucomutase catalyzes the reversible transfer of a phosphoryl group from the 1 or 6 position of glucose 1,6 diphosphate to a serine hydroxyl group on the enzyme yielding a phosphoenzyme intermediate... 

Fig. 7. Modes of binding of the intermediate glucose 1,6 diphosphate to phospho-glucomutase consistent with the geometry of Fig. 6. The enzyme bound Mn2+ promotes the nucleophilicity of the serine hydroxyl group and provides a pivot for the interchange of the 1 and 6 phosphoryl groups between the phosphoryl transfer and phosphoryl positioning sites...

Many starches contain small proportions of phosphorus which is not solvent-extractable but is present as phosphate ester of the C-6-hydroxyl group of a few n-glucose residues. Potato starch contains about 0.1% of phosphorus, most of which (0.08%) is present in the amylopectin component. Cereal starches may contain only 0.02% of phosphorus. The origin of the phosphorus in potato starch is not known. One possibility, wliich has not been examined experimentally, is that traces of n-glucose 1,6-diphosphate are incorporated into the polysaccharides by P-enzyme or by starch-UDPglucosyl transferase. 

The overall isomerization reaction presumably requires the intermediate glucose-1,6-diphosphate to either dissociate from the enzyme and rebind in a different configuration, or to reorient itself within the active site. 

In ah initio calculations, the species was modeled separately with MgFj and with P03 as the central moiety. " In the case of MgFj , an energy minimum was obtained with a geometry that corresponded well with the X-ray structure. When modeled as P03 the species is unstable, and resembles instead a transition state for phosphoryl transfer (with a moderate barrier of 14kcalmol ) from substrate G6P to the product glucose-1,6-diphosphate. The computationally modeled reaction is concerted with no phosphorane intermediate. ... 

D-ribose l-diphosphate,5-phosphate <38> (<38> activation, kinetics, much more effective than fructose 1,6-diphosphate or glucose 1,6-diphosphate [5]) [5]... 

Climent, E Carreras, M. Carreras, J. Metabolism of glucose 1,6-diphos-phate. 1. Enzymes involved in the synthesis of glucose 1,6-diphosphate in pig tissues. Comp. Biochem. Physiol. B Comp. Biochem., 81, 737-742 (1985)... 

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