Classes pyruvate kinase

Since the discovery that glycolate was an alternate substrate for pyruvate kinase ( ), several other o-hydroxy acids have also been found to be substrates for this enzyme ( ). This class of alternate substrates provides a new approach the problem of substrate specificity for pyruvate kinase. 3-Nitrolactate is one such alternate substrate. Interestingly, the phosphorylated product of this reaction inactivates the enzyme (86). However, 3-nitrolac-tate does not behave as a straightforward affinity label since covalent modification occurs nonspecifically. It is hoped that this new Information may lead to the design of an affinity label of this enzyme, further serving to pinpoint amino acid groups at the active site. 

Kemptide, H-Leu-Arg-Arg-Ala-Ser-Leu-Gly-OH, a synthetic 7-peptide substrate related to a partial sequence of the phosphorylation site in porcine liver pyruvate kinase. Kemptide is phosphorylated in vitro and in vivo by cAMP-dependent protein kinase, and in vitro by protein kinase C. Recently, kemptide has been used for the development of a new class of kinase microarray for the detection of kinase inhibition [B. E. Kemp et al.. Fed. Proc. 1976, 35, 1384 J. Zhou, J. A. Adams, Biochemistry 1997, 336, 15733 L. Sun et al. Anal. Chem. 2007, 79, 773]. 

The pyruvate dehydrogenase El subunit is a tetramer of two classes of subunits. The a-subunit catalyzes the decarboxylation of pyruvate to hydroxy-ethylthiamine diphosphate and the 8-subunit catalyzes the reductive acylation of the lipoamide prosthetic group of the acetyltransferase subunit. In the complete multienzyme complex, there are 20 (kidney) or 30 (heart) dehydrogenase tetramers, 60 acetyltransferase subunits, 10 (kidney) or 12 (heart) dihydroUpoyl dehydrogenase subunits, and 5 each of the kinase and phosphatase regulatory subunits. 

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