Rearrangement of the amino-acid residues in peptides by the action of proteolytic enzymes.

Abstract

MANY studies of the structure of proteins are based on enzymatic hydrolysis. Since methods of determining the order of the amino-acids in a peptide chain have been developed1, it is important to know whether the enzymatic hydrolysis gives products in which the sequence of the amino-acid residues is the same as in the parent protein. The possibility that enzymes bring about a rearrangement has been raised by Bergmann and Fraenkel-Conrat2, who showed that transamidation occurred. Thus, by the action of papain, hippuric anilide was formed more rapidly from aniline and hippuric amide than from aniline and hippuric acid. Similarly, Fruton showed that, by transamidation, isotopically labelled ammonia was incorporated in certain amides in the presence of papain3,4. It has recently been found5 that glutathione reacts with amino-acids to give their γ-glutamyl derivatives; this transpeptidation was brought about by an extract of sheep kidney.