An ESR Study of Secondary Radical Reactions in an Irradiated Sulfur-Containing Glycoprotein

Abstract

Solid yeast invertase has been irradiated in vacuum at 77 K and subsequently heated. The kinetics of formation of a secondary radical have been studied by following its growth at different temperatures. Progressive power saturation studies have been applied to determine (T/sub 1/T/sub 2/)/sup 1/2/ for the primary and secondary radical populations. It is shown that two different carbon radical populations constitute the primary and secondary species. Thus, (T/sub 1/T/sub 2/)/sup 1//sub 2// measured at 77 K increased from 1.0 to 1.7 ..mu..sec as a result of secondary radical reactions. Both the primary and secondary radical populations have g factors characteristic of carbon radicals. No evidence for organosulfur radicals was found for the cystine-containing glycoprotein, invertase. There was evidence for radical transformation in a period of little total radical decay. The principal secondary radical was formed with apparent activation energies of about 12 and 17 kcal/mole. These values are thought to represent upper limits of the true secondary radical energies of activation.