β-MERCAPTOPYRUVATE SULFUR TRANSFERASE DEFICIENCY.THE ENZYME DEFECT IN β-MERCAPTOLACTATE CYSTEINE DISULFIDURIA

Abstract

The disorder β-mercaptolactate cysteine disulfiduria was first identified in 1968 (Crawhall et al, Science 160: 419), and was thought to be an abnormality in cysteine metabolism. Current understanding of cysteine metabolism indicates that cysteine is mainly degraded to inorganic sulfate (60-80% total urinary sulfur). Thiosulfate constitutes <1% of the total sulfur output. In the latter case cysteine is first converted to β-mercapto-pyruvate (βMP) by transamination. The transfer of sulfur of βMP to sulfite to form thiosulfate, or to other anions is mediated by βMP sulfur transferase. A deficiency of this enzyme activity could be the cause of β-mercaptolactate cysteine dlsulfiduria. βMP sulfur transferase activity was thus studied in the blood cells of the original patient. Hemolysates were prepared in 0.02M cysteamine, and 0.025M phosphate buffer, pH 7.4. The assay condition was modified from that described by Sörbo. Activity of βMP sulfur transferase averaged 2.70 mmoles thiosulfate formed/gmHb/hr (range: 2.27 to 3.53) in 9 control hemolysates but was not detectable in the hemolysate from the patient (<5% of control values).

Presumably the liver enzyme is likewise deficient in this patient and this defect causes accumulation of βMP which is excreted as β-mercaptolactate cystetne dlsulfide.

Log in or create a free account to read this content

Gain free access to this article, as well as selected content from this journal and more on nature.com

Access through your institution

or

Sign in or create an account

Continue with Google

Continue with ORCiD