RIBONUCLEASE INHIBITOR PROTEIN OF HUMAN ERYTHROCYTES - CHARACTERIZATION, LOSS OF ACTIVITY IN RESPONSE TO OXIDATIVE STRESS, AND ASSOCIATION WITH HEINZ BODIES

Significant amounts of ribonuclease inhibitor protein are present in h uman and rat erythrocytes, cells that are essentially devoid of ribonu clease or functional RNA. The protein from human erythrocytes is indis tinguishable from human placental ribonuclease inhibitor protein by im munological and biochemical criteria. Each inhibitor forms an equimola r complex with bovine pancreatic ribonuclease A and is inactivated by treatment with the sulfhydryl reagent p-(hydroxymercuri)benzoate. Amin o acid composition and several cycles of amino acid sequence analysis also showed apparent identity of the erythrocyte and placental protein s. We calculate a level of 1.5 - 3.5 x 10(4) molecules of active inhib itor per erythrocyte, most or all of which occurs in an uncomplexed fo rm since inactivation of the inhibitor revealed barely detectable leve ls of RNase activity. Immunogold localization showed a high level of l abeling and a uniform distribution of gold particles in the cytoplasm of erythrocytes, while little inhibitor activity was found in associat ion with isolated red blood cell membranes. Oxidative stress on isolat ed red cells resulted in a decrease in the level of reduced glutathion e and a gradual and irreversible loss of inhibitor activity; inhibitor disappeared from the cytosol and became associated with nascent Heinz bodies, PI Te suggest a role for this protein in the metabolism and a ging process of the erythrocyte. (C) 1998 Academic Press.