Inactivation of myocardial dihydrolipoamide dehydrogenase by myeloperoxidase systems: Effect of halides, nitrite and thiol compounds

• Published in: Free radical research 1999-01, Vol.30 (2), p.105-117
• Main Authors: Gutierrez-Correa, J., Stoppani, A.O.M.
• Format: Article
• Language: English
• Subjects: Amino Acids - pharmacology; Animals; Binding Sites; Bromides - metabolism; Catalase - metabolism; Chlorides - metabolism; Dihydrolipoamide dehydrogenase; Dihydrolipoamide Dehydrogenase - antagonists & inhibitors; Dihydrolipoamide Dehydrogenase - metabolism; halides; Humans; Hydrogen Peroxide - metabolism; Hydrogen-Ion Concentration; hypochlorous acid; Hypochlorous Acid - pharmacology; Iodides - metabolism; myeloperoxidase; Myocardium - enzymology; nitrite; peroxidase; Peroxidase - antagonists & inhibitors; Peroxidase - metabolism; Sodium Nitrite - metabolism; Sulfhydryl Compounds - metabolism; Superoxide Dismutase - metabolism; Swine; Taurine - pharmacology; Thiocyanates - metabolism; thiol compounds
• ISSN: 1071-5762; 1029-2470
• DOI: 10.1080/10715769900300111

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 horseradish peroxidase suplemented 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.