Effect of oxygen on bacteria and cultured mammalian cells irradiated in the frozen state.

The oxygen effect for bacteria and cultured mammalian cells at -196 degrees C was studied, using suspensions to which were added cryoprotective and chemical protective agents. The oxygen enhancement ratio (o.e.r.) in the frozen state was dependent on the chemicals added to the suspensions. When the chemicals had a high competitive reactivity with oxygen to the damage, the o.e.r. in the frozen state was comparable to that in the liquid suspensions. Without chemicals, the o.e.r. in the frozen state decreased significantly, probably because of the low competitive activity of endogenous SH compounds. In general, the systems with a higher o.e.r. in the liquid state had a lower o.e.r. in the frozen state.