Studies on pituitary adrenocorticotrophin. 3. Identification of the oxidation–reduction centre

Abstract

The products of tryptic digestion of corticotrophin A1 and oxidized corticotrophin have been separated and compared by chromatography on carboxymethylcellulose. Only the N-terminal peptides differed significantly. The amino acid composition of the N-terminal peptides has been determined. The oxidized hormone differs in the substitution of methionine present in the untreated material. The amino acid composition of Raney-nickel-treated corticotrophin has been investigated after leucine aminopeptidase hydrolysis. Contrary to the findings of earlier studies on acid hydrolysates, methio-mine is still present in the material. On the basis of these studies and the correlation between biological activity and the extent of oxidation of methionine, it is concluded that the oxidation-reduction center of corticotrophin A1 is the thioether grouping of methionine.