Mannose-1,6-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. 

Figure 47-7. Pathway of biosynthesis of dolichol-P-P-oligosaccharide. The specific linkages formed are indicated in Figure 47-8. Note that the first five internal mannose residues are donated by GDP-mannose, whereas the more external mannose residues and the glucose residues are donated by dolichol-P-mannose and dolichol-P-glucose. (UDP, uridine diphosphate Dol, dolichol P, phosphate UMP, uridine monophosphate GDP, guanosine diphosphate M, mannose G, glucose.)...

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... 

This enzyme [EC 2.7.7.13], also known as GTP-mannose-1-phosphate guanylyltransferase, catalyzes the reaction of GTP with a-D-mannose 1-phosphate to produce GDP-mannose and pyrophosphate (or, diphosphate). The bacterial enzyme can also use ITP and dGTP as the phospho-ryl donors. 

R7. Richards, J. B., Evans, P. J., and Hemming, F. W., Dolichol phosphates as acceptors of mannose from guanosine diphosphate mannose in liver systems. Biochem. J. 124, 957-959 (1971). 

Fig. 4. Scheme depicting the order of interactions of enzyme with substrates. E denotes enzyme R-P represents PPi, carbamyl-P, nucleosidetriphosphate, nucleoside-diphosphate, or mannose-6 P. [Modified from Arion and Nordlie (ifi). 1... 

Nao S, Yoshio N, Yasuo Y et al (2002) Guanosine diphosphate-4-keto-6-deoxy-D-mannose reductase in the pathway for the synthesis of GDP-6-deoxy-D-talose in Actinobacillus actinomycetemcomitans. Eur J Biochem 269 5963-5971... 

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