Abstract
Abstract 1. 1. An enzyme capable of hydrolysing the dipeptide l -cysteinyl- l -tyrosine has been purified 60-fold from bovine-thyroid tissue by means of acetone fractionation, precipitation with zinc acetate and chromatography on calcium phosphate and diethylaminoethyl-cellulose. 2. 2. The purified “cysteinyltyrosinase” ( l -cysteinyl- l -tyrosine hydrolase) was found to hydrolyse a wide range of peptides but was substantially free from proteinase activity as tested against haemoglobin. 3. 3. Preliminary studies with cysteinyltyrosine, leucyltyrosine and leucylglycine suggest that only one enzyme is involved in the hydrolysis of these peptides. 4. 4. Enzymic activity can be inhibited by ethylenediamine tetraacetate and restored by the addition of Zn 2+ and to a lesser extent by Mn 2+ . 5. 5. No evidence was found for the hydrolysis of thyroglobulin by cysteinyltyrosinase leading to the formation of iodinated amino acids, although an enzyme preparation showing high proteinase and low cysteinyltyrosinase activities did effect such release.
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