The linkage of catalysis and regulation in enzyme action: oxidative diversion in the hysteretically regulated yeast pyruvate decarboxylase.
The reaction catalyzed by the thiamin-diphosphate-dependent yeast pyruvate decarboxylase, which is hysteretically regulated by pyruvate, undergoes paracatalytic oxidative diversion by 2,6-dichlorophenolindophenol, which traps a carbanionic intermediate and diverts the product from acetaldehyde to acetate (Christen, P. Meth. Enzymol. 1977, 46, 48). This reaction is now shown to exhibit an oxidant on-rate constant somewhat faster than that for pyruvate in the normal catalytic cycle and a product off-rate constant about 60-fold smaller than that for acetaldehyde. Both on-rates and off-rates exhibit an inverse solvent isotope effect of 1.5-2, observed in normal catalysis as a signal of sulfhydryl addition to the keto group of pyruvate at the allosteric regulatory site. The findings are consistent with a model for regulation in which the sulfhydryl-addition process mediates access to a fully catalytically competent active site, the oxidative-diversion reaction being forced to make use of the normal entry exit machinery.
Hajipour
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G
Department of Chemistry and Higuchi Biosciences Center, University of Kansas, Lawrence 66047, USA.
Schowen
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KB
Schowen
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RL
D015086:2,6-Dichloroindophenol / Q000494:pharmacology; D000494:Allosteric Regulation; D001665:Binding Sites; D002384:Catalysis; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D008956:Models, Chemical; D010100:Oxygen / Q000378:metabolism*; D011767:Pyruvate Decarboxylase / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology
D015086:2,6-Dichloroindophenol; D011767:Pyruvate Decarboxylase; D010100:Oxygen