Glucose-6-phosphate formation

The large and negative value for hexokinase indicates that this enzyme catalyses the reaction only in the direction of glucose 6-phosphate formation, i.e. it is a non-equilibrium reaction in vivo. In contrast, the low value for phosphoglucoisomerase indicates that it is a reaction that is close to equilibrium in vivo, that is, it can proceed in either direction. AG valnes for all the reactions of glycolysis indicate that those catalysed by hexokinase, phosphorylase, phos-phofractokinase and pyrnvate kinase are non-eqnilibrinm the others are near eqnilibrinm (Fignre 2.6). 

Williams JF, Clark MG, Arora KK, Reichstein IC. Glucose 6-phosphate formation by L-pentose pathway reactions of rat liver in vitro-, further evidence. Hoppe Seyler s Zeit. Fur Biochemie. 1984 365 1425-1434. 

KInatM enzymes which catalyse the transfer of a phosphate residue (strictly speaking a phosphoryl group is transferred) from ATP to another substrate, in particular to the alcoholic hydroxyl groups of monosaccharides. Some important K. are hexokinase, which phosphorylates several hexoses at the C6 position, glucokinase, which is responsible for glucose 6-phosphate formation in the liver, and phosphofructo-kinase. 

If we take some recently isolated mitochondria, add some ADP to reinforce the natural content, glucose and hexokinase to trap the phosphate of newly formed ATP as glucose-6-phosphate, and an oxidisable substrate such as pyruvate or other organic acid of the Krebs cycle, it is possible to demonstrate active phosphorylation. Further, by measuring glucose-6-phosphate formation and oxygen... 

This pathway is variously known as the pentose phosphate, hexose monophosphate or phosphogluconate pathway, cycle or shunt. Although the pentose phosphate pathway achieves oxidation of glucose, this is not its function, as indicated by the distribution of the pathway in different tissues. Only one of the carbons is released as CO2, the key products are NADPH and ribose 5-phosphate, both of which are important for nucleotide phosphate formation and hence for synthesis of nucleic acids (Chapter 20). The... 

The energy stored in the a(l 4) glycosidic bond during the condensation reaction in glycogen synthesis is sufficient to permit the formation of a glucose-phosphate bond without using ATP. 

Figure 2 The relationship between the maximum activity of phosphoglucomutase-metal-glucose phosphate complexes and (a) the ionic radius of the metal ion, and (b) the structural change produced on formation of the complex (Reproduced by permission from J. Biol. Chem., 1969, 244, 3754)...

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