ACTIONS OF RADIATIONS ON ENZYMES

I. BIOCHEMICAL EFFECTS OF GAMMA RADIATION ON UREASE

Abstract

1. The inactivating mechanism of enzyme by X-ray irradiations proposed by Dale and Barron et al. was reconfirmed with the effect of γ-rays on urease.
2. Urease is proved to be more sensitive in its aqueous solution than in an air dried state.
3. Urease in aqueous solutions is found to be protected against γ-ray inactivation by the presence of several substances such as sodium chloride, glycine, ovalbumin, especially reduced glutathione and cysteine.
4. By small doses of γ-irradiations inactivation of urease is reversibly relieved by the reducing agents, such as reduced glutathione or cysteine. In this case, oxidation of essential sulfhydryl groups in the enzyme molecules by radiation products of water is causative of its inactivation.
5. Urease is less sensitive against γ-ray at pH at which the enzyme shows its optimal activity.
6. Larger doses of γ-ray irradiations cause formation of ammonia in urease solutions and consequent irreversible inactivation of the enzyme activity. Inactivation of this type is attributed to chemical changes occurring in the enzyme molecule, such as the radiolytic breakdown of peptide bonds followed by the oxidative deamination of its component amino acids.