Deficiencies of cystathionase and homoserine dehydratase activities in cystathioninuria.

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Abstract
Cystathionase activity was markedly reduced in an extract from the liver of a patient with Idlopathic cysta-thioninurla. Activities of methionine activating enzyme and cystathionine synthase were within the normal range in this extract. A sensitive, radiochemical assay for homoserine dehydratase has been developed. By use of this assay, the liver extract from the cystathionnuric patient was shown to be deficient also in homoserine dehydratase. The ratio of homoserine dehydratase/cystathionase activities in liver extracts is relatively constant, a finding which is consistent with the hypothesis that the 2 activities are properties of a single enzyme. The cystathionase activity of the extract from the liver of the patient with cystathioninuria was not stimulated more than were controls by the In vitro addition of pyridoxal phosphate. The role of pyridoxal phosphate in this syndrome is discussed.