Distribution of sulfur in urine of patients with cystathioninuria before and during administration of pyridoxine

During administration of 400 mg daily of vitamin B 6 as pyridoxine hydrocholoride to two patients with homozygous cystathioninuria, cystathionine excretion fell in a characteristic manner. Inorganic sulfate excretion did not change significantly when considered by itself. Total sulfur excretion, determined as sulfate after oxidation, decreased slightly in both patients and this decrease was statistically significant in one. The ratio of sulfate to total sulfur excretion increased significantly in both patients during vitamin B 6 administration. The difference between total sulfur and free plus bound or ethereal sulfate is largely accounted for by cystathionine and lesser amounts of N-acetyl-cystathionine. The results indicate that cystathionine sulfur is not excreted other than as sulfate during vitamin B 6 administration and support the hypothesis that cystathionase activity is enhanced by pyridoxine, the resultant cysteine, α-ketobutyrate, and ammonia being added to large body pools.