The oxygen effect in radiation inactivation of DNA and enzymes.

A survey is made of literature data dealing with the influence of oxygen on radiation effects in biologically active DNA and enzymes irradiated extracellularly. There is evidence that oxygen takes part in physico-chemical events, directly or indirectly produced by radiation in several ways: from scavenging reducing primary water radicals to reacting directly with macromolecular radical sites. There is evidence that radiation-induced secondary radicals, originating from a variety of low molecular weight biomolecules, can react with DNA and enzymes in their native state, and produce inactivation. By reaction with oxygen secondary radicals become peroxidized and in this form are generally more harmful to biological macromolecules. There are indications that thiol peroxy radicals can also act in the same way. Possible implications for the oxygen effect observed in vivo are discussed.