The degradative metabolism of l-cysteine and l-cystine in vitro by liver in cystinosis

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Abstract
Autopsy samples of liver from 3 cases of cystinosis were compared with normal liver with respect to the degradative metabolism of cystine and cysteine, with particular emphasis on the enzymic reduction of cystine. Under the conditions of these experiments the reduction of cystine to cysteine by cystine reductase and by glutathione-cysteine transhydrogenase was normal in cystinotic liver. Also, no abnormality was found in the cystine-reductase activity of kidney. Glutathione-reductase activity and reduced glutathione content of cystinotic liver were normal. Cysteine, cystine and cysteinesulphinate were completely oxidized by liver of the cystinosis cases, and these findings were substantiated by the normal urinary excretion of inorganic sulphate by cystinosis patients. The liberation of hydrogen sulphide from cysteine and cystine by cystinotic liver was normal, the reactivity of cystine depending on its prior reduction to cysteine. No abnormality of cystinotic liver was observed for the transamination of cysteine, cysteic acid and cysteinesulphinic acid with a-oxoglutarate. Normal decarboxylation of cysteic acid and cysteinesulphinic acid was observed for cystinotic liver. These findings are discussed with respect to the etiology of cystinosis.