Further studies on the activation of acid proteinase in human erythrocyte membranes: Evidence for an activator in the membranes

Abstract

Acid proteinase in human erythrocyte membranes is thought to play important roles in physiological and pathological breakdown of the membrane proteins. However, no acid proteinase activity has been detectable in sealed ghosts and inside-out vesicles from the membranes in the absence of detergents. It is not known whether the latent enzyme represents an enzyme-inhibitor complex or a zymogen. In any case, the most important factor which controls activity of the latent enzyme seems to be a specific activator in the erythrocyte. The present study was undertaken to clarify the existence of an activator for the enzyme in the membranes. The purified enzyme was incubated with the proteinase-depleted inside-out vesicles (Brij -shells) from the erythrocyte membranes at 0 °C for 60 min. The enzyme activity was markedly increased in proportion to the amounts of Brij -shells and then attained the saturated value. No activation was observed by heated Brij -shells. In addition, Brij -shells which were extensively washed with 20 mM phosphate buffered saline (pH 8.0) showed a decrease in activation of the enzyme. These results indicate the existence of a heat-unstable activator for acid proteinase in human erythrocyte membranes.