Renal cysteine conjugate beta-lyase. Bioactivation of nephrotoxic cysteine S-conjugates in mitochondrial outer membrane.
Cysteine conjugate beta-lyase activity from rat kidney cortex was found in the cystosolic and mitochondrial fractions. With 2 mM S-(2-benzothiazolyl)-L-cysteine as the substrate, approximately two-thirds of the total beta-lyase activity was present in the cytosolic fraction. The kinetics of beta-lyase activity with three cysteine S-conjugates were different in the cytosolic and mitochondrial fractions, and the mitochondrial beta-lyase was much more sensitive to inhibition by aminooxyacetic acid than was the cytosolic activity. These results indicate that the beta-lyase activities in the two subcellular fractions are catalyzed by distinct enzymes. Nephrotoxic cysteine S-conjugates of halogenated hydrocarbons that require bioactivation by cysteine conjugate beta-lyase (S-(1,2-dichlorovinyl)-L-cysteine (DCVC), S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine, CTFC) were potent inhibitors of state 3 respiration in rat kidney mitochondria. Fractionation of mitochondria by digitonin treatment and comparison with marker enzyme distributions showed that the mitochondrial beta-lyase activity is localized in the outer mitochondrial membrane. Inhibition of the beta-lyase prevented the mitochondrial toxicity of DCVC and CTFC, and nonmetabolizable, alpha-methyl analogues of DCVC and CTFC were not toxic. Neither DCVC nor CTFC was toxic to mitoplasts, indicating that activation by the beta-lyase occurs on the outer membrane and may be essential for the expression of toxicity; in contrast, the direct acting nephrotoxin S-(2-chloroethyl)-DL-cysteine was toxic to both mitochondria and mitoplasts. Thus, the suborganelle localization of DCVC and CTFC bioactivation correlates with the observed pattern of toxicity.
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D000818:Animals; D013437:Carbon-Sulfur Lyases; D002458:Cell Fractionation; D003600:Cytosol / Q000201:enzymology; D004789:Enzyme Activation; D007425:Intracellular Membranes / Q000201:enzymology; D007672:Kidney Cortex / Q000201:enzymology*; D007700:Kinetics; D008190:Lyases / Q000378:metabolism*; D008297:Male; D008928:Mitochondria / Q000201:enzymology*; D010101:Oxygen Consumption; D051381:Rats; D011916:Rats, Inbred F344; D013347:Subcellular Fractions / Q000201:enzymology / Q000648:ultrastructure
D008190:Lyases; D013437:Carbon-Sulfur Lyases; C019969:S-alkylcysteine lyase