Phosphoglucomutase, reactions involving

The phosphoglucomutase reaction involves continual utilization and resynthesis of the cofactor, but it cannot cause the net synthesis of glucose-1,6-diphosphate. Two mechanisms have been found to increase the amount of this cofactor in each case glucose-l-phosphate is the phosphate acceptor but the phosphate donors are different for the two enzymes involved. Glucose-l-phosphate kinase requires ATP to carry out the reaction ... 

The glucose-1-phosphate formed in reaction 2 is then converted to glucose-6-phosphate by phosphoglucomutase (reaction 4), an enzyme involved also in glycogen biosynthesis. Nucleoside diphosphate sugars such as UDP-glucose are widely used intermediates in polysaccharide biosynthesis. 

Fig. 19.3. The phosphoglucomutase reaction. The forward direction is involved in converting glucose to glycogen, and the reverse direction in converting glycogen to glucose 6-P.

This reaction, which can be catalyzed by phosphoglucomutase, has been studied in detail by Klenow and co-workers (21-25). They demonstrated that the reaction involves ribose 1,5-diphosphate as an obligatory inter-... 

The involvement of methionine sulfonium salts in these chemical cleavage reactions may stimulate experiments to show the significance of special methionine residues in the active centers and the catalytic sites of enzymes. Such an important role for a particular methionine has been postulated for the enzymes phosphoglucomutase and chymotrypsin on the basis of photooxidation studies (Ray et al., 1960). 

Some of the uncertainty about the transition state of the reaction of some enzymes, like p-phosphoglucomutase-catalyzed transfer of a phosphoryl group to a substrate in sugar metabolism, was resolved recently. Allan and Dunaway demonstrated that by means of nuclear magnetic resonance that the transition state involved a bipyramidal oxyphosphorane intermediate [72]. 

The phosphoglucomutase enzyme catalyzes reaction 79. Reaction 78, which involves an inversion (Walden inversion) at C4 of the hexose, was shown to require a heat-stable cofactor. s This coenzyme for the galactowaldenase system was isolated and its structure determined. The coenzyme is uridinidiphosphoglucose (UDPGlucose). 

The end effect of mutases is to shift phosphate residues within a sugar molecule. In actual fact, several reactions are involved in which phosphorylated mutases take part. For example, phosphoglucomutase converts glucose-6-phosphate into glucose-1-phosphate by a phosphate shift. The existence of this enzyme in plants has not yet been proved. However, a number of reactions, which have been observed, presuppose its existence. 

In this laboratory two enzymes, phosphoglucomutase and a UDP-glucose pyrophosphorylase, have been demonstrated in cell free extracts of S. niveus (BC-345) which could catalyze the initial steps necessary in the reaction mechanism described above. In the pyrophosphorylase reaction, no other nucleotide triphosphate tested (TTP, CTP, GTP or ATP) would substitute for uridine triphosphate (UTP). The possible involvement of UDP-glucose in the formation of the noviose moiety of novobiocin is currently being studied in this laboratory. 

It is known that certain cell constituents are involved in the reversible activation and inactivation of enzymes. Thus, the enzyme phosphoglucomutase which catalyses the reaction... 

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