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Abstract

The widespread occurrence of the pentose phosphate pathway in living cells testifies to the importance of this metabolic route, whose primary functions are: a) the production of pentose phosphate for mono-, di- and polynucleotide synthesis; b) the formation of NADPH to be used by the cell in a variety of biosynthetic pathways and reductive processes. The control of the pentose phosphate cycle is not yet fully understood; regulatory mechanisms are likely to operate at the initial step (the glucose 6-phosphate reaction). The activity of hepatic glucose 6-phosphate dehydrogenase is inhibited by NADPH. The experiments confirm that the inhibition by NADPH is competitively reserved by NADP and depends on the [NADPH] / [NADP+] ratio. However, other factors must overcome the inhibition by NADPH, and in this sense glutation has been proposed. Several observations have indicated that the activity of the glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase is regulated by the nutritional and hormonal state of the animal. Enzyme activity increases when an animal is starved and re-fed with a high-carbohydrate diet, or after administration of insulin or glucocorticoids. In addition, the dietary induction of these enzyrnes is regulate in a fashion that is coordinate with other lipogenic enzymes. Also, sorne features of the renal pentose phosphate pathway are discussed.