Catalyzes the desulfonation and deamination of L-cysteate, yielding pyruvate, sulphite and ammonium. Is involved in a L-cysteate degradation pathway that allows Silicibacter pomeroyi to grow on L-cysteate as the sole source of carbon and energy. To a lesser extent, can also act on D-cysteine in vitro, leading to the production of pyruvate, sulfide and ammonium. L-cysteine, L-cysteine sulfinate, and 1-aminocyclopropane-1-carboxylate (ACC) are not substrates for the enzyme. H2O + L-cysteate = H(+) + NH4(+) + pyruvate + sulfite Optimum pH is 8.8-9.0. Homomultimer, maybe a homotrimer. Expressed in cells grown on L-cysteate, but not on acetate or taurine. Cotranscribed with cuyZ, with which it is likely to form an operon. Belongs to the ACC deaminase/D-cysteine desulfhydrase family.