DIRECT OBSERVATION OF DIFFERENTIAL UV PHOTOLYTIC DEGRADATION AMONG THE TRYPTOPHAN RESIDUES OF GRAMICIDIN-A IN SODIUM DODECYL-SULFATE MICELLES

Gramicidin A, incorporated into sodium dodecyl sulfate micelles, was e xposed to ultraviolet light and discovered by two-dimensional (TOCSY) NMR spectroscopy to undergo differential photolytic degradation. The f our tryptophan residues of gramicidin A were found to be unequally sen sitive to ultraviolet radiation. Tryptophan 9 was the most sensitive t o ultraviolet photolysis, while tryptophan 11 was the least sensitive. Tryptophans 13 and 15 have approximately the same susceptibility to p hotolytic degradation by the ultraviolet light. Rate constants for the photolytic degradation of the four tryptophan residues were obtained from the dependence of the TOCSY spectrum upon the time of photolysis.