The iodination of chymotrypsinogen

Abstract

The iodination of tyrosine, histidine and their simple peptides with iodine in ammonia and with iodine monochloride has been studied by using radioactive iodine. With iodine in ammonia mono- and di-iodo derivatives are formed with both residues, whereas with iodine monochloride histidine is converted only into the monoiodo derivative. Treatment of the non-radioactive iodo derivatives with radioactive iodine leads to the incorporation of the label by exchange reactions. Iodination of native chymotrypsinogen with iodine monochloride occurs preferentially at one tyrosine residue which is present in the sequence Thr-Arg-Tyr. Similar results are obtained with native chymotrypsin. The substitution on the readily iodi-natable residue does not appear to involve loss in enzymic activity.