Glyceraldehyde-3-phosphate dehydrogenase reaction catalyzed

Analyses of enzyme reaction rates continued to support the formulations of Henri and Michaelis-Menten and the idea of an enzyme-substrate complex, although the kinetics would still be consistent with adsorption catalysis. Direct evidence for the participation of the enzyme in the catalyzed reaction came from a number of approaches. From the 1930s analysis of the mode of inhibition of thiol enzymes—especially glyceraldehyde-phosphate dehydrogenase—by iodoacetate and heavy metals established that cysteinyl groups within the enzyme were essential for its catalytic function. The mechanism by which the SH group participated in the reaction was finally shown when sufficient quantities of purified G-3-PDH became available (Chapter 4). 

Glyceraldehyde-3-phosphate dehydrogenase (NADP+) (phosphorylating) [EC 1.2.1.13], also known as triose-phosphate dehydrogenase (NADP+), catalyzes the reaction of D-glyceraldehyde 3-phosphate with orthophosphate and NADP to produce 3-phospho-D-glyceroyl phosphate and NADPH. 

FIGURE 4.60 Oxidation of an aldehyde group to a carboxylic acid group. The smiling face represents the glyceraldehyde-3-phosphate dehydrogenase, happily catalyzing its reaction in the presence of an ample amount of NAD". ... 

Chloroplast glyceraldehyde Phosphate dehydrogenase Catalyzes reactions in the Calvin cycle, glucose synthesis... 

Thus far, we have considered enzyme-catalyzed reactions involving one or two substrates. How are the kinetics described in those cases in which more than two substrates participate in the reaction An example might be the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (Chapter 19) ... 

The spectral characteristics of the NADH model [20] are analogous to NADH bound to glyceraldehyde-3-phosphate dehydrogenase. The acid-catalyzed hydration (3) of [20] is affected by the micelles the reaction is... 

The formation of ATP (or GTP) at the expense of the energy released by the oxidative decarboxylation of a-ketoglutarate is a substrate-level phosphorylation, like the synthesis of ATP in the glycolytic reactions catalyzed by glyceraldehyde 3-phosphate dehydrogenase and pyruvate kinase (see Fig. 14-2). The GTP formed by succinyl-CoA synthetase can donate its terminal phosphoryl group to ADP to form ATP, in a reversible reaction catalyzed by nucleoside diphosphate kinase (p. 505) ... 

In addition, hepatic fatty acid oxidation is also required to sustain gluconeogenesis. These fatty acids may be obtained from exogenous feeding or metabolism of fatty acids released from endogenous lipid stores. (3-Oxidation of fatty acids provides the acetyl-CoA needed to activate mitochondrial pyruvate carboxylase and the NADH used as the substrate in the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase in the direction of gluconeogenesis (see Fig. 10-1). 

No, because an important omission is inorganic phosphate. Even if phosphate were added to the incubation mixture, pyruvate would be produced only in an amount equivalent to that of the NAD+ present. Glycolysis requires NAD+ for Step 6, the reaction catalyzed by glyceraldehyde-3-phosphate dehydrogenase. 

Thus, the outcomes of the reactions catalyzed by glyceraldehyde 3-phosphate dehydrogenase and phosphoglycerate kinase are ... 

FIGURE 4.62 Regeneration of NAD". The concentration of cytoplasmic NAD can be maintained by a reaction, by the concomitant reduction of pyruvate, catalyzed by lactate dehydrogenase (LDH). This permits continued action of glyceraldehyde-3-phosphate dehydrogenase. Once again, the enzyme is happy. 

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