Glucose 6-phosphogluconate

Heterolactic fermentation pathway of glucose (6-phosphogluconate/phosphoketolase pathway]... 

Metabolic Functions. The formation of phosphate esters is the essential initial process in carbohydrate metaboHsm (see Carbohydrates). The glycolytic, ie, anaerobic or Embden-Meyerhof pathway comprises a series of nine such esters. The phosphogluconate pathway, starting with glucose, comprises a succession of 12 phosphate esters. 

Cells require a constant supply of N/ X)PH for reductive reactions vital to biosynthetic purposes. Much of this requirement is met by a glucose-based metabolic sequence variously called the pentose phosphate pathway, the hexose monophosphate shunt, or the phosphogluconate pathway. In addition to providing N/VDPH for biosynthetic processes, this pathway produces ribos 5-phosphate, which is essential for nucleic acid synthesis. Several metabolites of the pentose phosphate pathway can also be shuttled into glycolysis. 

The dehydrogenase catalysing the glucose-6-phosphate to 6-phosphogluconate step is specific for the phosphorylated derivative of gluconate. 

Bishop, C. Assay of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in red cell. J. 

D8. Dickens, F., and Glock, G. E., Direct oxidation of glucose-6-phosphate, 6-phosphogluconate and pentose-5-phosphate by enzymes of animal origin. Biochem. ]. 50, 81-95 (1951). 

G10. Glock, G. E., and McLean, P., Further studies on the properties and assay of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase of rat liver. Biochem. ]. 55, 400-408 (1953). 

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 three reactions are catalysed by glucose 6-phosphate Glucose enters the blood from three different sources dehydrogenase, gluconolactonase and phosphogluconate depending on the conditions. 

The oxidative pentose phosphate pathway (phosphogluconate pathway, or hexose monophosphate pathway) brings about oxidation and decarboxylation at C-l of glucose 6-phosphate, reducing NADP+ to NADPH and producing pentose phosphates. 

Chayen, J., Howat, D.W., Bitensky, L. (1986) Cellular biochemistry of glucose 6-phosphate and 6-phosphogluconate dehydrogenase activities. Cell Biochem. Fund. 4, 249-253. 

Reactions of the hexose monophosphate pathway. Enzymes numbered above are 1) glucose 6-phosphate dehydrogenase and 6-phosphogluconolactone hydrolase, 2) 6-phosphogluconate dehydrogenase,... 

---