Mutase Phosphoglucomutase

The glucose 6-phosphate thus formed can enter glycolysis or another pathway such as the pentose phosphate pathway, described in Section 14.5. Phosphoglucomutase employs essentially the same mechanism as phos-phoglycerate mutase (p. 531). The general name mu-tase is given to enzymes that catalyze the transfer of a functional group from one position to another in the same molecule. Mutases are a subclass of isomerases, enzymes that interconvert stereoisomers or structural or positional isomers (see Table 6-3). 

Phosphoenolpyruvate phosphomutase Phosphoglucomutase Phosphoglycerate mutase (co-factor independent) Phosphoglycerate mutase (co-factor dependent)... 

Why are the mechanisms of the enzymes that interconvert glucose-6-phosphate and fructose-6-phos-phate and the enzyme that interconverts dihydroxyac-etone phosphate and glyceraldehyde-3-phosphate virtually identical Compare the mechanisms of phosphoglycerate mutase and phosphoglucomutase. Why are they so similar ... 

Mutase Transfer of phosphoryl group between sites on substrate Phosphoglucomutase (glucose-6-phosphate glucose-1-phosphate) ... 

Carreras, J., F. Climent, R. Bartrons, and G. Pons. 1982. Effect of vanadate on the formation and stability of the phosphoenzyme forms of 2,3-bisphosphoglycerate-dependent phosphoglycerate mutase and of phosphoglucomutase. Biochim. Biophysic. Acta 705 238-242. 

With the purified enzyme, the phosphoglucomutase reaction is several hundred times faster than the phospho-D-glucosamine mutase reaction. ... 

Pig-kidney extracts have some phospho-iV-acetyl-D-glucosamine mutase activity. The ratio of phosphoglucomutase to phospho-AT-acetyl-n-glucos-amine mutase activity is 60 1 in these extracts. In rabbit muscle, this ratio i is 1200 1. Phosphoglucosamine mutase activity was not checked in any of the phosphomutase preparations investigated by this worker. 

In contrast to phosphohydrolases, the phosphatase activity of enzymes which non-hydrolytically catalyse the transfer of phosphate groups can be stimulated by vanadate. Vanadate can spontaneously form esters with unphosphorylated substrates such as sugars. These vanadate esters act as alternative substrates for mutases and isomerases, stimulating their phosphatase activity. Examples are phosphoglucomutase, which catalyses the mutation (phosphate shift) between glucose-1-phosphate and glucose-6-phosphate, and phosphoribose isomerase, which catalyses the isomerisation between ribose-5-phosphate and ribulose-5-phosphate.P ]... 

PGMs are named for the anomer of GIP on which they act a-phosphoglucomutase (a-PGM) acts on the a-C(l) anomer of GIP, while /3-PGM catalyzes the reaction of the /3-C(l) anomer. Both mutases employ Mg as a cofactor. 

Klenow concluded that both phosphoglucomutase and phosphoiibomutase activities reside in a single protein the ratio of the two activities remained constant during purification of the enzyme from muscle, both activities were stimulated by Mg and cysteine, both exhibited the same pH optimum, and both were inhibited by inorganic anions. On the other hand, Guarino and Sable 26, 27) have purified a specific phosphoiibomutase from uterine muscle this mutase showed no requirement for divalent cations. At the present time, it is difficult to evaluate the relative physiological significance of the two mutases in the interconversion of the ribose phosphates. 

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. 

A special kind of isomerization moves a group from one position to another position in the same compound. These kinds of isomerases are called mutases. The conversion of a-Glc-1-P into Glc-6-P is catalyzed by phosphoglucomutase. Another example is the transfer of the phosphate group from position 3 of 3-phos-pho-D-glycerate to position 2 to give 2-phospho-D-glycerate, catalyzed by phos-pho-D-glycerate mutase. 

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