title: Inactivation of human lactate dehydrogenase isozymes by sulfhydryl reagents.
abstract: Human lactate dehydrogenase isozymes, LDH-1 and LDH-5, were inactivated at 25 degrees C and pH 7.5 by N-alkylmaleimides of varying chain length, and by fluorescein mercuric acetate. Second-order rate constants for the inactivation of LDH-5 by N-alkylmaleimides increased with increasing chain length of the maleimide derivative while essentially no chain-length effect was observed in the inactivation of LDH-1. Both isozymes were effectively inactivated by low concentrations of fluorescein mercuric acetate, and in both cases saturation kinetics were observed. Dissociation constants obtained from double-reciprocal plotting methods indicated a twofold better binding of fluorescein mercuric acetate to LDH-1. Protection from fluorescein mercuric acetate by NAD was observed with both enzymes.
mesh_terms: D005452:Fluoresceins / Q000494:pharmacology; D006801:Humans; D007527:Isoenzymes; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000037:antagonists & inhibitors*; D009941:Organomercury Compounds / Q000494:pharmacology; D013329:Structure-Activity Relationship; D013439:Sulfhydryl Reagents / Q000494:pharmacology*
chemical_list: D005452:Fluoresceins; D007527:Isoenzymes; D009941:Organomercury Compounds; D013439:Sulfhydryl Reagents; C001673:fluorescein mercuric acetate; D007770:L-Lactate Dehydrogenase