Relationship of catalase and sodium nitrite to protection against X-rays

Abstract

The ability of sodium nitrite to protect various biological systems against X-rays has been attributed to several mechanisms, one of which, enhancement of the ability of catalase to decompose hydrogen peroxide, has been investigated with bacteriophage T1. In order to establish the validity of using catalase as a protective agent for phage against X-rays, the ability of catalase to withstand X-irradiation was determined under the conditions of these experiments, and the sensitivity of bacteriophage T1 to hydrogen peroxide was established. The phage was then irradiated in the presence of varying concentrations of catalase and of sodium nitrite, and of the two combined. High protection was afforded the phage by high concentrations of catalase and of nitrite, with gross protection falling off rapidly when low concentrations of solutes were employed although specific protection (protection per microgram of solute) was increased. In the presence of the two protective agents combined, there was impairment rather than enhancement of the ability of catalase to protect T1 against X-rays. The impaired activity is explained by increased peroxidatic action, which proceeds at the expense of the catalatic action, of catalase. In the catalatic reaction, hydrogen peroxide acts as both substrate and donor molecule, and the velocity constant for the reaction with hydrogen peroxide as donor is many times greater than with nitrite as donor. Sodium nitrite does not enhance the protective ability of catalase for irradiated T1, nor does it enhance the ability of catalase to decompose hydrogen peroxide; nevertheless, nitrite alone is an efficient protector, acting presumably as a reducing agent.