Trypanosoma cruzi dihydrolipoamide dehydrogenase is inactivated by myeloperoxidase-generated "reactive species"

Dihydrolipoamide dehydrogenase (LADH) from Trypanosoma cruzi was inactivate d by treatment with myeloperoxidase (MPO)-dependent systems. With MPO/H2O2/ NaCl, LADH lipoamide reductase and diaphorase activities significantly decr eased as a function of incubation time. Iodide, bromide, thiocyanide and ch loride effectively supplemented the MPO/H2O2 system, KI and NaCl being the most and the least effective supplements, respectively. LADH inactivation b y MPO/H2O2/NaCl and by NaOCl was similarly prevented by thiol compounds suc h as GSH, L-cysteine, N-acetylcysteine, penicillamine and N-(2-mercaptoprop ionyl-glycine) in agreement with the role of HOCl in LADH inactivation by M PO/H2O2/NaCl. LADH was also inactivated by MPO/NADH/halide, MPO/H2O2/NaNO2 and MPO/NADH/NaNO2 systems. Catalase prevented the action of the NADH-depen dent systems, thus supporting H2O2 production by NADH-supplemented LADH. MP O inhibitors (4-aminobenzoic acid hydrazide, and isoniazid), GSH, L-cystein e, L-methionine and L-tryptophan prevented LADH inactivation by MPO/H2O2/Na NO2. Other MPO systems inactivating LADH were (a) MPO/H2O2/chlorpromazine; (b) MPO/H2O2/monophenolic systems, including L-tyrosine, serotonin and acet aminophen and (c) MPO/H2O2/di- and polyphenolic systems, including norepine phrine, catechol, nordihydroguaiaretic acid, caffeic acid, quercetin and ca techin. Comparison of the above effects and those previously reported with pig myocardial LADH indicates that both enzymes were similarly affected by the MPO-dependent systems, allowance being made for T. cruzi LADH diaphoras e inactivation and the greater sensitivity of its LADH lipoamide reductase activity towards the MPO/H2O2/NaCl system and NaOCl.