Glutamine transaminase K is not a major cysteine S-conjugate beta-lyase of rat kidney mitochondria: evidence that a high-molecular weight enzyme fulfills this role.

Glutamine transaminase K (homodimer; M(r) of monomer approximately 45,000) is a major cysteine S-conjugate beta-lyase of rat kidney cytosol. Several cysteine S-conjugates are known to cause kidney damage. Mitochondria are especially sensitive, and glutamine transaminase K activity is present in the mitochondrial fraction of rat kidneys. Therefore, it is possible that the mitochondrial form of glutamine transaminase K is a cysteine S-conjugate beta-lyase of the rat kidney and that this activity contributes to the mitochondrial damage. However, the literature contains conflicting data on this point. We obtained highly purified mitochondrial glutamine transaminase K and showed that it possesses little cysteine S-conjugate beta-lysae activity with S-(1,2-dichlorovinyl)-L-cysteine and S-(1,1,2,2-tetrafluoroethyl)-L-cysteine as substrates. Recently, a high-molecular-weight cysteine S-conjugate beta-lyase (M(r) approximately 330,000) was shown to be present in the cytosol of rat kidney homogenates and partially purified. We present evidence that suggests that a similar high-molecular-weight enzyme is present in rat kidney mitochondria and that this protein may be a major cysteine S-conjugate beta-lyase of these organelles.