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 <tex-math>$(T_{1}T_{2})^{{\textstyle\frac{1}{2}}}$</tex-math> for the primary and secondary radical populations. It is shown that two different carbon radical populations constitute the primary and secondary species. Thus, <tex-math>$(T_{1}T_{2})^{{\textstyle\frac{1}{2}}}$</tex-math> measured at 77 K increased from 1.0 to 1.7 μsec 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.

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