Treponema denticola cystalysin catalyzes beta-desulfination of L-cysteine sulfinic acid and beta-decarboxylation of L-aspartate and oxalacetate.

Pyridoxal 5'-phosphate-dependent cystalysin from Treponema denticola catalyzes the beta-displacement of the beta-substituent from both L-aspartate and L-cysteine sulfinic acid. The steady-state kinetic parameters for beta-desulfination of L-cysteine sulfinic acid, k(cat) and K(m), are 89+/-7 s(-1) and 49+/-9 mM, respectively, whereas those for beta-decarboxylation of L-aspartate are 0.8+/-0.1 s(-1) and 280+/-70 mM. Moreover, cystalysin in the pyridoxamine 5'-phosphate form has also been found to catalyze beta-decarboxylation of oxalacetate as shown by consumption of oxalacetate and a concomitant production of pyruvate. The k(cat) and K(m) of this reaction are 0.15+/-0.01 s(-1) and 13+/-2 mM, respectively. Possible mechanistic and physiological implications are discussed.