INFLUENCE OF OSMOTIC-STRESS ON PROTEIN METHYLATION IN RESEALED ERYTHROCYTES

Resealed erythrocytes are a useful means of targeting exogenous protei ns or extending their activity. We tested human resealed erythrocytes as a model system for studying protein methyl esterification, a reacti on involved in the processing of spontaneously deamidated/isomerized p olypeptides. Our results show that resealed erythrocytes are still act ive in the metabolic processes that lead to the formation of methyl-es terified proteins. The methylation pattern of endogenous membrane prot eins appeared to be similar to that of normal erythrocytes, with bands 2.1, 3, 4.1 and 4.2 as the major methyl accepters. We detected methyl esterification of ovalbumin, as an exogenous substrate trapped within resealed erythrocytes. Methyl incorporation was almost completely inh ibited by simultaneously loading red cells with adenosine and homocyst eine thiolactone, in vivo precursors of the transmethylation inhibitor S-adenosyl-homocysteine. We investigated the effects of repeated rese aling procedures on methyl acceptability of endogenous membrane protei ns. We found that methyl-incorporation levels increased, despite an ap parent conserved protein composition of the membrane. This result sugg ests that osmotic stress to the membrane may be responsible for increa sed protein methylation due to the appearance of new sites or an incre ased accessibility of existing sites.