Define Role of Glucose-6-phosphate dehydrogenase - Gene Expression?
Glucose-6-phosphate dehydrogenase (G6PD) is another enzyme involved in lipogenesis that is regulated by dietary factors. G6PD activity is needed in all cell types for the production of NADPH and for the control of carbon flow through the pentose phosphate pathway. G6PD catalyzes the first reaction of this pathway, oxidizing glucose-6- hosphate to 6-phosphogluconolactone , and in the process reducing NADP' to NADPH+ H+. This reaction, you may recall studying, is the rate-determining step of the oxidative portion of the pentose phosphate pathway. Together with 6- phosphogluconolactone dehydrogenase, the enzyme provides NADPH for reductive biosynthetic reactions, such as fatty acids, cholesterol and amino acids and for the maintenance of reduced glutathione concentration. In addition, it regulates the rate of glucose conversion to ribose-5-phosphate, the precursor for nucleotide biosynthesis. G6PD expression is regulated by hormonal and nutritional factors in a few tissues such as the liver and mammary glands.
Long-term starvation decreases the activity of the enzyme, while re-feeding with a fat free; high-carbohydrate increases the activity to an amount greater than in the "normal" fed state. Glucose and fructose increase activity to a larger extent than starch and the response is greater with fructose than with glucose.