title: Role of sulfhydryl groups in benzoquinone-induced Ca2+ release by rat liver mitochondria.
abstract: Incubation of rat liver mitochondria with benzoquinone derivatives in the presence of succinate plus rotenone has been shown to cause NAD(P)H oxidation followed by Ca2+ release. Further investigation revealed: (1)p-Benzoquinone-induced Ca2+ release was not initiated by a collapse of the mitochondrial membrane potential. However, Ca2+ release and subsequent Ca2+ cycling caused limited increased membrane permeability. (2) p-Benzoquinone-induced NAD(P)H oxidation and Ca2+ release were prevented by isocitrate, 3-hydroxybutyrate, and glutamate but not by pyruvate or 2-oxoglutarate. (3) Inhibition of pyruvate and 2-oxoglutarate dehydrogenases by p-benzoquinone was attributed to arylation of the SH groups of the cofactors, CoA and lipoic acid. Isocitrate dehydrogenase was also inhibited by p-benzoquinone, but the cofactors NAD(P)H and Mn2+ protected the enzyme. Glutamate dehydrogenase was not inhibited by p-benzoquinone. (4) Arylation of mitochondrial protein thiols by p-benzoquinone was associated with an inhibition of state 3 respiration, which was attributed to the inactivation of the phosphate translocase. In contrast, state 4 respiration, and the F1.F0-ATPase and ATP/ADP translocase activities were not inhibited. It was concluded that inhibition of mitochondrial NAD(P)H dehydrogenases by arylation of critical thiol groups will decrease the NAD(P)+-reducing capacity, and possibly lower the NAD(P)H/NAD(P)+ redox status in favor of Ca2+ release.
authors.affiliation: Department of Toxicology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: G A
authors.initials: GA
authors.lastname: Moore
authors.forename: M
authors.initials: M
authors.lastname: Weis
authors.forename: S
authors.initials: S
authors.lastname: Orrenius
authors.forename: P J
authors.initials: PJ
authors.lastname: O'Brien
mesh_terms: D000818:Animals; D016227:Benzoquinones; D002118:Calcium / Q000378:metabolism*; D004137:Dinitrochlorobenzene / Q000494:pharmacology; D007521:Isocitrate Dehydrogenase / Q000037:antagonists & inhibitors; D007658:Ketone Oxidoreductases / Q000037:antagonists & inhibitors; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000201:enzymology; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D011809:Quinones / Q000494:pharmacology* / Q000633:toxicity; D051381:Rats; D011919:Rats, Inbred Strains; D013438:Sulfhydryl Compounds / Q000378:metabolism*
chemical_list: D016227:Benzoquinones; D004137:Dinitrochlorobenzene; D011809:Quinones; D013438:Sulfhydryl Compounds; C004532:quinone; D009249:NADP; D007521:Isocitrate Dehydrogenase; D007658:Ketone Oxidoreductases; D002118:Calcium