PROFLAVINE‐SENSITIZED PHOTOOXIDATION OF TRYPTOPHAN AND RELATED PEPTIDES

— The photodynamic action of proflavine on the amino acids cystine, rnethionine, tyrosine, histidine, tryptophan and related peptides was tested in anhydrous formic and acetic acids. Only rnethionine and tryptophan were found to be photooxidized: the former, whether free or bound in a polypeptide chain, is quantitatively converted to methioninesulphoxide; the latter, when free, is fragmented to several compounds, which may be divided into two main classes: melanines and kynurenine derivatives. Whereas masking the carboxyl group of tryptophan has no effect on the photooxidation products, N-substituted derivatives of tryptophan are converted in high yields to the corre-sponding kynurenine compounds. The possible applications of the method to biologically active polypeptides are discussed.