Phosphoglucomutase phosphate pathway

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). 

Phosphoglucomutase converts glucose-l-phosphate into glucose-6-phosphate which has several metabolic fates. It is for example a precursor in the pentose phosphate pathway (PPP), it can be converted to a-D-glucose and to pyruvate via the glycolysis pathway (see Figure 9.2). 

G6P is a phosphorylated form of glucose commonly found in cells. G6P is an intermediate in glycolysis, gluconeogenesis, the pentose phosphate pathway, the Calvin Cycle, glycogen biosynthesis, glycogen breakdown, and sugar interconversion. The latter three pathways indirectly involve G6P via the enzyme phosphoglucomutase. 

Phosphoglucomutase converts glucose 1-phosphate to glucose 6-phosphate, which enters the pathway of glycolysis and is converted either to lactate or to C02 and H20, generating ATP. 

Scheme 5 Representations of the four enzyme-substrate complexes on the reaction pathway of phosphoglucomutases (PGMs). G1P, glucose-1 -phosphate G6P, glucose-6-phosphate. The a-PGMs utilize the a-anomers at Cl, and a serine as the phosphoryl carrier. The /3-PGMs utilize the /3-anomers at 01 and an aspartate as the phosphoryl carrier.

Fig. 20.5 The Leloir pathway of galactose metabolism and the uridine diphosphate (UDP) glucose pyrophosphorylase pathway. Gaik, galactokinase gait, galactose 1-phosphate uridyltrans-ferase gale, UDP-galactose 4-epimerase hex, hexokinase pgm, phosphoglucomutase Ugp, UDP-glucose pyrophosphorylase...

These conclusions were based on advanced isotopic studies showing that if fructose-1 is converted to fructose-6-phosphate, it can go directly to glycogen through the isomerase and phosphoglucomutase reaction without first being split into trioses. Under those conditions, all the of the hexoses entering the glycogen molecule will be recovered in carbon 1, and this is precisely what happens in muscle. In liver, the label of the fructose-1 is randomized why this happens will become obvious when the pathway for fructose-1-phosphate has been outlined. 

Fig. 14.2 Cellulose biosynthetic pathway in cellulose-producing acetic acid bacteria. FIP firuc-tose-1-phosphate, F6P fructose-6-phosphate, FDP fructose diphosphate, PGA phosphogluconate GHK glucose hexokinase, FHK fructose hexokinase, IPFK fructose-1-phosphate kinase, FBP fructose blsphosphatase, PGI phosphoglucose isomerase, PGM phosphoglucomutase, UGP UDP-glucose pyrophosphorylase, G6PD glucose-6-phosphate dehydrogenase, PTS phosphotransferase system EMP Embden-Myerhoff pathway...

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