Primary Processes in the Flash Photolysis of Ovalbumin and Constituents

Abstract

It is well known that the absorption of ultraviolet light by proteins induces significant permanent changes in almost all measurable properties (1). The purpose of these experiments is to investigate the primary photochemical acts by means of the flash photolysis of ovalbumin and certain constituent amino acids and related compounds. Flash photolysis work with simpler compounds has shown that aromatic free radicals can be detected, owing to resonance stabilization, thus suggesting that the lifetimes of free radical intermediates of amino acids and proteins might also be sufficiently long for detection (2). The experimental method, in brief, consists in irradiating with an intense light flash the air-free solutions in a fused silica cell and then, after a preset time interval, taking the optical absorption spectrum with a weaker lamp as the source. In this way, one obtains the absorption spectrum of the transient photochemical products within 10 ,usec of flash irradiation. For most of these experiments, the irradiation flash lamp duration was 25 ,/sec, with a maximum effective light output of 5 X 1019 quanta, from 200 to 500 mui, into a 35-cc sample in a 25-cm-long cell. The absorption spectra were taken with a 10-.isec-duration spectroflash lamp on the Gaertner L 234 quartz prism spectrograph using Kodak 103-F spectroscopic plates. The concentrations of solute were chosen to give an optical density of unity for a 1-cm path at the peak of the aromatic absorption band (e.g., 1 mM phenol in H20). The chemicals used were analytical grade and were not further purified. Other experimental details are reported elsewhere (3).