Pyridoxal 5′-phosphate-dependent cystalysin from Treponema denticola catalyzes the β-displacement of the β-substituent from both L-aspartate and L-cysteine sulfinic acid. The steady-state kinetic parameters for β-desulfination of L-cysteine sulfinic acid, kcat and K m, are 89±7 s-1 and 49±9 mM, respectively, whereas those for β-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 β-decarboxylation of oxalacetate as shown by consumption of oxalacetate and a concomitant production of pyruvate. The kcat and Km of this reaction are 0.15±0.01 s-1 and 13±2 mM, respectively. Possible mechanistic and physiological implications are discussed. © 2003 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.
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