Pyruvate dehydrogenase phosphorylation

Huang, YJ., Walker, D., Chen, W., Klingbeil, M. and Komuniecki, R. (1998b) Expression of pyruvate dehydrogenase isoforms during the aerobic/anaerobic transition in the development of the parasitic nematode, Ascaris suum altered stoichiometry of phosphorylation/inactivation. Archives of Biochemistry and Biophysics 352, 263-270. 

Klingbeil, M.M., Walker, D.J., Huang, YJ. and Komuniecki, R. (1997) Altered phosphorylation/inactivation of a novel pyruvate dehydrogenase in adult Ascaris suum muscle. Molecular and Biochemical Parasitology 90, 323-326. 

Korotchkina, L.G. and Patel, M.S. (1995) Mutagenesis studies of the phosphorylation sites of recombinant human pyruvate dehydrogenase. Site-specific regulation. Journal of Biological Chemistry 270, 14297—14304. 

Thissen, J. and Komuniecki, R. (1988) Phosphorylation and inactivation of the pyruvate dehydrogenase from the anaerobic parasitic nematode, Ascaris suum. Stoichiometry and amino acid sequence around the phosphorylation sites. Journal of Biological Chemistry 263, 19092-19097. 

Where two enzymes compete for the same substrate, we expect to see some form of metabolic control and in this case the concentrations of NADH and acetyl-CoA are the key controlling factors (Figure 6.44). When glucose is not available as a fuel, metabolism switches to 3- oxidation of fatty acids, which generates more than sufficient quantities of both NADH and acetyl-CoA to drive the TCA cycle and to maintain oxidative phosphorylation. Pyruvate dehydrogenase activity is suppressed and pyruvate carboxylase is stimulated by ATP, NADH and acetyl-CoA (strictly speaking by low mitochondrial ratios of ADP/ATP, NAD+/NADH and coenzyme A/acetyl-CoA), so... 

Many enzymes in the mitochondria, including those of the citric acid cycle and pyruvate dehydrogenase, produce NADH, aU of which can be oxidized in the electron transport chain and in the process, capture energy for ATP synthesis by oxidative phosphorylation. If NADH is produced in the cytoplasm, either the malate shuttle or the a-glycerol phosphate shuttle can transfer the electrons into the mitochondria for delivery to the ETC. Once NADH has been oxidized, the NAD can again be used by enzymes that require it. 

Mitochondria are also described as being the cell s biochemical powerhouse, since—through oxidative phosphorylation (see p. 112)—they produce the majority of cellular ATP. Pyruvate dehydrogenase (PDH), the tricarboxylic acid cycle, p-oxidation of fatty acids, and parts of the urea cycle are located in the matrix. The respiratory chain, ATP synthesis, and enzymes involved in heme biosynthesis (see p. 192) are associated with the inner membrane. 

Covalent interconversion of enzymes is well established as a fundamental theme in metabolic regulation. The prototypic reversible interconverting systems include the sequence of phosphorylation/dephosphorylation steps in the activation of mammalian glycogen phosphorylase and pyruvate dehydrogenase as well as the nucleotidyla-tion/denucleotidylation using UTP and ATP in the bacterial glutamine synthetase cascade (see Fig. 1.). 

This enzyme [EC 2.7.1.99] catalyzes the reaction of ATP with [pyruvate dehydrogenase (lipoamide)] to produce ADP and [pyruvate dehydrogenase (lipoamide)] phosphate. This is an enzyme that is associated with the pyruvate dehydrogenase complex. Phosphorylation of pyruvate dehydrogenase (lipoamide) [EC 1.2.4.1] inactivates that enzyme. 

Thiamine (vitamin Bi) is phosphorylated by ATP to thiamine pyrophosphate. This is a coenzyme for, among others, alpha-ketoglutarate dehydrogenase, transketolase and pyruvate dehydrogenase. Thiamine pyrophosphate is involved in fatty acid... 

ATP 4- pyruvate dehydrogenase <2> (<2> PDH is phosphorylated and inactivated in vitro and also in /)A-treated hippocampal cultures, resulting in mitochondrial dysfunction which will contribute to neuronal death [7]) (Reversibility <2> [7]) [7]... 

TABLE 16-1 Stoichiometry of Coenzyme Reduction and ATP Formation in the Aerobic Oxidation of Glucose via Glycolysis, the Pyruvate Dehydrogenase Complex Reaction, the Citric Acid Cycle, and Oxidative Phosphorylation... 

Experiments with rats have shown that the branched-chain a-keto acid dehydrogenase complex is regulated by covalent modification in response to the content of branched-chain amino acids in the diet. With little or no excess dietary intake of branched-chain amino acids, the enzyme complex is phosphorylated and thereby inactivated by a protein kinase. Addition of excess branched-chain amino acids to the diet results in dephosphoiylation and consequent activation of the enzyme. Recall that the pyruvate dehydrogenase complex is subject to similar regulation by phosphorylation and dephosphorylation (p. 621). 

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