Alterations in proteins and polyamino acids caused by ultraviolet irradiation in a spectropolarimeter

The Xenon lamp in a Cary 60 spectropolarimeter caused a photochemical reaction in proteins and polyamino acids which was traced to cleavage in the polypeptide chains. Viscosity studies on helical and coiled polyamino acids indicated that the cleavage occurred in both forms, but ORD changes were obtained only with helical and not with coiled and β conformations. Proteins of high helix content exhibited a significant change in ORD which was enhanced in the presence of denaturants. Quantum yields based on ORD change were greater in the n→Π ∗ than in the Π→Π ∗ transition region.