Pyruvate dehydrogenase enzymatic activity

Acetyl-CoA is a potent allosteric effector of glycolysis and gluconeogenesis. It allosterically inhibits pyruvate kinase (as noted in Chapter 19) and activates pyruvate carboxylase. Because it also allosterically inhibits pyruvate dehydrogenase (the enzymatic link between glycolysis and the TCA cycle), the cellular fate of pyruvate is strongly dependent on acetyl-CoA levels. A rise in... 

Within many tissues the enzymatic activities of the pyruvate and branched chain oxoacid dehydrogenases complexes are controlled in part by a phosphorylation -dephosphorylation mechanism (see Eq. 17-9). Phosphorylation of the decarboxylase subunit by an ATP-dependent kinase produces an inactive phosphoenzyme. A phosphatase reactivates the dehydrogenase to complete the regulatory cycle (see Eq. 17-9 and associated discussion). The regulation is apparently accomplished, in part, by controlling the affinity of the protein for... 

Aside from PEPCase, a number of other CAM-related genes have been partially characterised (Table 1). These include cDNA clones for pyruvate, orthophosphate dikinase (PPDK), a specific NADP malate dehydrogenase (MDH), glyceraldehyde phosphate dehydrogenase (GaPDH) and NADP-dependent malic enzyme (MOD). Previous studies indicated that the enzymatic activities of these gene products increased upon salt stress in the ice plant (Holtum Winter, 1982). As in the case... 

Enzymatic activities contained in the pyruvate dehydrogenase complex include ... 

Like the pyruvate dehydrogenase complex, the alpha-ketoglutarate dehydrogenase complex has three enzymatic activities, and the same cofactors. As might be expected, the primary sequences of the proteins are highly similar, indicating that they diverged from a common set of ancestral proteins. 

Direct, nonmediated electrochemical reduction of NADIP)" " at modified electrode surfaces has been used to produce the en2ymatically active NAD(P)H and even to couple the NAD(P)H regeneration process with some biocatalytic reactions [228]. The modifier molecules used for these purposes are not redox active and they do not mediate the electron-transfer process between an electrode and NAD(P)+ however, they can effectively decrease the required overpotential and prevent formation of the nonenzymatically active dimer product [228]. For example, the efficiency of the direct electrochemical regeneration of NADH from NAD" " was enhanced by the use of a cholesterol-modified gold amalgam electrode that hinders the dimerization of the NAD-radicals on its modified-surface [228]. This direct electrochemical NAD+ reduction process was used favorably to drive an enzymatic reduction of pyruvate to D-lactate in the presence of lactate dehydrogenase. The turnover number for NAD" " was estimated as 1400 s k Other modifiers that enhance formation of the enzymatically active NAD(P)H include L-histidine [229] and benzimidazole [230], immobilized as monolayers on silver electrodes. CycKc voltammetric experiments demonstrated that these modified electrodes can catalyze the reduction of NAD+ to enzymatically active NADH at particularly low overpotentials. 

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