Background Numerous studies have shown that the intracellular redox potential of
ID: 89559 • Letter: B
Question
Background Numerous studies have shown that the intracellular redox potential of the cell is important to cell growth. Cellular redox potential can be determined by the amounts of the reduced coenzyme NADPH, a principal product of the oxidative branch of the pentose phosphate pathway (PPP). The investigators in the study presented here sought to demonstrate links between the activity of the enzyme glucose-6-phosphate dehydrogenase (G6PD) activity, cellular NADPH concentrations, and rates of cell growth. Previous studies have shown that the glucose-6- phosphate dehydrogenase enzyme can be activated on the order of minutes or even seconds, possibly through the action of growth factors that release a bound, inactive G6PD to the cytosol, where, via a mechanism that might involve tyrosine phosphorylation of a membrane-bound receptor, the unbound G6PD translocates to the cytosol and becomes active. NADPH is important to the cell in a variety of ways. The reduced coenzyme can react with potential damaging oxidizing agents, ridding the cell of these agents before they can damage 2 2 important cellular components. For example, hydrogen peroxide, H O , may be reduced to water with concomitant oxidation of NADPH
question #7
7. The authors of this study have shown that platelet derived growth factor (PGDF) stimulates the release of G6PD to the cytosol, and that this release depends on tyrosine phosphorylation of PGDF. They believe that it is likely that phosphatidylinositol-3-kinase (PI-3-kinase) and phospholipase C-Y are involved. Draw a diagram that shows the sequence of events involved in the release and subsequent activation of G6PDExplanation / Answer
Glucose-6-phosphate dehydrogenase catalyzes the first step in the pentose phosphate shunt and also involved in oxidising glucose-6-phosphate (g-6-p)to 6-phosphogluconate(6-pg) and reducing NADP to NADPH.
G-6-P + NADP+ 6-PG+ NADPH + H+
NADP is reduced by G-6-PDH in the presence of G-6-P. The rate of formation of NADPH is directly proportional to the G-6-PDH activity and is measured absorbance level as an increased in absorbance at 340nm. Second molar equivalant of NADPH by erythrocyte 6-phosphogluconate dehydrogenase (6-PGDH) according to the reaction :
l6-PG + NADP+ = Ribulose-5- phosphate + NADPH + H+ + CO2
NADPH is important to the cell in a various ways. The reduced coenzyme can react with potential damaging oxidizing agents and also ridding the cell of these agents before they will damage the important cellular components.
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