ISOLATION FROM RAT-KIDNEY OF A CYTOSOLIC HIGH-MOLECULAR-WEIGHT CYSTEINE-S-CONJUGATE BETA-LYASE WITH ACTIVITY TOWARD LEUKOTRIENE E(4)

A cytosolic high M(r) cysteine-S-conjugate beta-lyase (apparent M(r) o f similar to 330,000) has been partially purified from rat kidneys. Th e high M(r) lyase is also present in the mitochondria, The purified en zyme contains at least two proteins with apparent M(r) values of simil ar to 50,000 and similar to 70,000. Activity is stimulated by dithioth reitol, alpha-keto acids, and pyridoxal 5'-phosphate; aminooxyacetate is an inhibitor. The enzyme catalyzes a competing (half) transaminatio n reaction between pyridoxal 5'-phosphate cofactor and cysteine-S-conj ugate substrate; added alpha-keto acids promote conversion of active s ite pyridoxamine 5'-phosphate to pyridoxal 5'-phosphate. The enzyme al so catalyzes a full (but weak) transamination between L-phenylalanine and alpha-keto-gamma-methiolbutyrate. The purified enzyme is not recog nized by polyclonal rabbit antibodies to cytosolic rat kidney glutamin e transaminase K (another cysteine-S-conjugate beta-lyase of rat kidne y) and has no obvious similarities to other pyridoxal 5'-phosphate-con taining enzymes. In addition to catalyzing elimination reactions with S-(1,2-dichlorovinyl)-L-cysteine and S-(1,1,2,2-tetrafluoroethyl)-L-cy steine, the enzyme reacts with leukotriene E(4) and 5'-S-cysteinyldopa mine. Finally, the cytosolic and mitochondrial enzymes are activated b y alpha-ketoglutarate. Thus, the possibility must be considered that, in kidneys of animals exposed to various cysteine conjugates, the high M(r) lyase contributes to the generation of pyruvate, ammonia, and re active fragments in vivo. Many cysteine conjugates are nephrotoxic, an d the high M(r) lyase(s) may be involved.