Abstract
Crystalline trypsin was irradiated with ultraviolet light of 254 nm in various oxygen-free suspension media at a temperature of 278 K. Using electron spin resonance spectroscopy long-living free radicals were detected in the enzyme. Unpaired electrons are mainly localized at Cα-atoms of the polypeptide chain and at the sulphur of damaged disulfide bridges. The ultraviolet irradiation of trypsin leads to greater yields of thiyl radicals RS · in nonpolar media than in polar ones. If the dielectric constant is chosen as a measure of polarity a relationship between the relative concentration of thiyl radicals [RS ·]rel and the dielectric constante in form of [RS ·]rel ∼ 1/e is obtained. The manner how the suspension media may influence the formation of thiyl radicals is discussed. The results allow the conclusion that the radiation-induced scission of disulflde bonds is of significance for the inactivation of trypsin.
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