Triose phosphate, oxidation, inhibition

Mn-SOD is an important antioxidant enzyme for the cell due to its role in detoxifying the free radical species superoxide (Oj), so HNE modification of this protein makes the cell more vulnerable to free radical attack. Alpha enolase facilitates the penultimate step of glycolysis by catalyzing the conversion of 2-phosphoglycerate into phosphoenolpyruvate. With HNE modification of alpha enolase, the cell is at risk of inadequate ATP stores due to inhibited production of pyruvate for fueling the citric acid cycle. Similarly, HNE modification of ATPase can lead to inhibited ATP formation due to the direct role of this enzyme in ATP synthesis. Triose phosphate isomerase catalyzes the reversible conversion of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate in glycolysis and MDH catalyzes the oxidation of malate to oxaloacetate, so HNE modification of these proteins can also lead to lower ATP production. 

A number of intermediates common to both the hexose monophosphate shunt and the glycolytic pathway are glucose-6-phosphate, fructose-6-phosphate, fructose-6,1-diphosphate, and triose phosphate. Thus, the two pathways can be expected to compete for intermediates, and, indeed, when a reconstituted glycolytic system made of purified enzymes is added to the reconstituted hexose monophosphate shunt, glucose oxidation by the shunt is inhibited by glycolysis. 

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