Open AccessPossible occurrence and role of an essential histidyl residue in succinate dehydrogenase.
Author(s) -
Steven B. Vik,
Youssef Hatefi
Publication year - 1981
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.78.11.6749
Subject(s) - succinate dehydrogenase , submitochondrial particle , chemistry , oxidoreductase , malonate , active site , stereochemistry , dehydrogenase , enzyme , hydroxylamine , biochemistry , residue (chemistry) , ferricyanide
Diethylpyrocarbonate (Et2PC) inhibits the succinate dehydrogenase [succinate:(acceptor) oxidoreductase, EC 1.3.99.1] activity of submitochondrial particles, Complex II (succinate:ubiquinone oxidoreductase), and the soluble, pure succinate dehydrogenase. The reaction order with respect to Et2PC concentration is close to unity, suggesting modification of one essential residue per active unit of the enzyme. The pH profile of Et2PC inhibition, the partial reversal of inhibition by hydroxylamine, and the spectral change of the Et2PC-treated enzyme in the UV region suggest modification of a histidyl residue. Succinate dehydrogenase activity can be protected against Et2PC inhibition by succinate, fumarate, malonate, or oxaloacetate (also by activating anions such as ClO4(-) and Br-), suggesting that the Et2PC-modified essential residue might be at the active site. In both submitochondrial particles and the purified enzyme, succinate dehydrogenase activity is highest and relatively constant at pH greater than or equal to 7.0 and diminishes precipitously at pH less than 7.0. By contrast, fumarate reductase activity is highest at pH less than or equal to 7.0 and diminishes at pH greater than 7.0. These results are consistent with the possible participation of the unprotonated and protonated forms of the imidazole moiety of the putative histidyl residue, respectively, in succinate oxidation and fumarate reduction.