The oxidation of cysteinesulfinic and cysteic acids in Proteus vulgaris

Abstract

1. 1. Thoroughly washed, resting cells of P. vulgaris OX-19 rapidly oxidize L- and D-cysteinesulfinic and L-cysteic acids. 2. 2. Optimal oxidation of L-cysteinesulfinate occurs at pH 8–8.6 at 0.05 M (or higher) substrate concentration. An initial lag in O 2 uptake is regularly observed, which appears to be associated with a transaminative reaction. Addition of 2 · 10 −3 M Mn ++ increses the oxidation of the L-amino acid markedly, but fails to decrease the lag period. Mn ++ is concerned with the removal of the primary reaction product of L-cysteinesulfinate. 3. 3. The differences in the characteristic features in the initial oxidation of L- and DL-cysteinesulfinate suggest that the primary enzymic reactions of the two optical antipodes are catalyzed by separate enzymes and may be different reactions. 4. 4. The initially rapid oxidation of L-cysteate comes to a halt after the uptake of less than 1 atom of O 2 per mole of substrate, while the oxidation of L-cysteinesulfinate continues until about 6 atoms of O 2 are utilized. 5. 5. The experimental observations have been interpreted in terms of a dual pathway for L-cysteinesulfinate metabolism. It involves an initial oxidation to cysteate by one route and a transamination with an α-keto acid by the other route; β-sulfinylpyruvic acid is then desulfinated to yield pyruvic acid and sulfite, and the latter yield CO 2, water, and sulfate.