Inhibition of sulfate excretion by (aminooxy)acetate induced stimulation of taurine excretion in rats.

L-Cysteine is mainly metabolized to sulfate and taurine through cysteinesulfinate pathway. Alternatively, sulfate is formed in rat liver mitochondria via 3-mercaptopyruvate pathway. Intraperitoneal administration of 5 mmol ofL-cysteine per kg of body weight resulted in the increase in sulfate and taurine (plus hypotaurine) excretion in the 24-h urine, which corresponded to 45.3 and 29.3%, respectively, ofL-cysteine administered. Subcutaneous injection of (aminooxy)acetate, a potent inhibitor of transaminases, together withL-cysteine halved the sulfate excretion and doubled the taurine excretion. In vitro sulfate formation fromL-cysteine and fromL-cysteinesulfinate in rat liver mitochondria was inhibited by (aminooxy)-acetate. The sulfate-forming activity of liver mitochondria obtained from rats injected with (aminooxy) acetate was also inhibited. These results indicate that the transamination reaction is crucial in sulfate formation and in the regulation of sulfur metabolism. Sulfur equilibrium in mammals was discussed.