Free radicals and protein degradation in human red blood cells.

Human red blood cells (RBC) were exposed to oxygen-based free-radicals, and other activated oxygen species generated during incubation with xanthine plus xanthine oxidase (X+XO). Oxygen-radical exposure induced up to 30 fold increases in human RBC protein degradation, compared to 12 fold increases in rabbit RBC protein degradation. Protein degradation increased as a function of X+XO, but demonstrated saturation kinetics at higher XO concentrations. The presence or absence of an energy substrate (glucose) had no effect on protein degradation, indicating the possible role of ATP-independent proteinolytic systems. It is proposed that human RBC proteins can be oxidatively damaged by certain free-radicals, and that the oxidized proteins are specifically recognized and degraded by intracellular proteinolytic systems.