Inactivation of myocardial dihydrolipoamide dehydrogenase by myeloperoxidase systems: effect of halides, nitrite and thiol compounds.
Dihydrolipoamide dehydrogenase (LADH) lipoamide reductase activity decreased whereas enzyme diaphorase activity increased after LADH treatment with myeloperoxidase (MPO) dependent systems (MPO/H2O2/halide, MPO/NADH/halide and MPO/H2O2/nitrite systems. LADH inactivation was a function of the composition of the inactivating system and the incubation time. Chloride, iodide, bromide, and the thiocyanate anions were effective complements of the MPO/H2O2 system. NaOCl inactivated LADH, thus supporting hypochlorous acid (HOCl) as putative agent of the MPO/H2O2/NaCl system. NaOCl and the MPO/H2O2/NaCl system oxidized LADH thiols and NaOCl also oxidized LADH methionine and tyrosine residues. LADH inactivation by the MPO/NADH/halide systems was prevented by catalase and enhanced by superoxide dismutase, in close agreement with H2O2 production by the LADH/NADH system. Similar effects were obtained with lactoperoxidase and horse-radish peroxidase supplemented systems. L-cysteine, N-acetylcysteine, penicillamine, N-(2-mercaptopropionylglycine), Captopril and taurine protected LADH against MPO systems and NaOCl. The effect of the MPO/H2O2/NaNO2 system was prevented by MPO inhibitors (sodium azide, isoniazid, salicylhydroxamic acid) and also by L-cysteine, L-methionine, L-tryptophan, L-tyrosine, L-histidine and reduced glutathione. The summarized observations support the hypothesis that peroxidase-generated "reactive species" oxidize essential thiol groups at LADH catalytic site.
Gutierrez-Correa
J
J
Bioenergetics Research Centre, School of Medicine, University of Buenos Aires, Paraguay, Argentina.
Stoppani
A O
AO
D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D001965:Bromides / Q000378:metabolism; D002374:Catalase / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D008058:Dihydrolipoamide Dehydrogenase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006997:Hypochlorous Acid / Q000494:pharmacology; D007454:Iodides / Q000378:metabolism; D009206:Myocardium / Q000201:enzymology*; D009195:Peroxidase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012977:Sodium Nitrite / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000378:metabolism; D013552:Swine; D013654:Taurine / Q000494:pharmacology; D013861:Thiocyanates / Q000378:metabolism
D000596:Amino Acids; D001965:Bromides; D002712:Chlorides; D007454:Iodides; D013438:Sulfhydryl Compounds; D013861:Thiocyanates; D013654:Taurine; D006997:Hypochlorous Acid; D006861:Hydrogen Peroxide; D002374:Catalase; D009195:Peroxidase; D013482:Superoxide Dismutase; D008058:Dihydrolipoamide Dehydrogenase; D012977:Sodium Nitrite