Abstract
1. Serine dehydratase [EC 4. 2. 1. 13] was purified 250 fold from livers of rats fed on a high protein diet.
2. Serine dehydratase activity was strongly and noncompetitively inhibited by elemental sulfur, one of the end products of the decom-position of L-cystine by cystine desulfurase.
3. Homoserine dehydratase and cysta-thionase were competitively inhibited by L-cysteine and L-cystine.
4. Regulatory mechanisms in the rat liver enzyme system converting L-methionine to L-cystine are discussed.
The authors gratefully acknowledge the excellent technical assistance given by Miss Toyoko Kawai.