Michael E. Jayko

Radiation-Chemical Oxidation of Peptides in the Solid State

Gamma-ray irradiation of polypeptides as highly dispersed fluffs under oxygen leads to chemical degradation of the peptide bond with the remarkably high oxygen consumption of about one molecule per 2 ev of absorbed energy. A radical chain mechanism appears to be involved, and there is evidence that excited states of the polypeptide aggregate undergo chemical quenching by molecular oxygen.

Growth factor studies; Changes in reactivity of sulfhydryl groups with activation

Abstract Observed changes in the reactivity of the essential sulfhydryl groups of a protein growth factor correlate with changes in its biological activity. In activated and non-activated growth factor, the maximal number of sulfhydryl groups reacting with parachloromercuribenzoate was the same; while the spatial arrangement of the sulfhydryl groups appeared to differ, as evidenced by their different rates of chemical reaction. It is believed that these changes in sulfhydryl reactivity reflect structural changes in the protein molecule and that these structural changes are responsible for the observed changes in its biological activity.

Activation of a growth factor by non-physiological means

Abstract A protein growth factor, which shows growth-controlling properties in a number of living systems, has been found to undergo reversible activation (up to thirty-fold) of its biological activity. Biological activity and the effects of activation have been shown by promoting growth in nematode cultures, certain strains of tissue cultures, an obligate serum-requiring bacterium and by influencing the rat of growth of transplanted tumors in animals. The growth factor is present in serum and other tissues of mammals, including man and also in certain bacteria that have been examined. Activation can be accomplished by a variety of non-physiological means, as well as by a natural activator present in serum. A physiological inhibitor of activation has also been isolated from human serum. The non-physiological procedures for activation and deactivation mimic, at least in end result, the physiological activator and inhibitor. These non-physiological activation and deactivation procedures are reported here as a guide to understanding the chemistry of physiological control of the biological activity of circulating growth factor. Evidence is presented indicating activation and deactivation of growth factor to result from reversible conformational changes within the protein molecule.

A sensitive chemical procedure for monitoring the radiolytic oxidation of proteins at γ-ray dosages down to 1 Krad

Abstract The radiolytic degradation of proteins in oxygenated solution is initiated by the attack of OH radicals at a multiplicity of main-chain and side-chain loci to give a wide variety of oxidized protein sites. A major fraction of these oxidation reactions lead to the introduction of reactive carbonyl groups into the protein co-valent structure. With γ-rays the total carbonyl yield correspond to G(>CO)t ≃ 1 for a number of different proteins. Outlined here is a sensitive chemical-spectrophotometric procedure for quantitatively monitoring G(>CO)t over a dose range of interest in radiation biology (1 to 50 Krad). Data obtained with pepsin, α-chymotryps in and β-lactoglobulin are discussed.