Erythrocyte membrane phosphorylation in aging rats

Abstract

By sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the protein profile and autophosphorylation of plasma membranes of red cells from 3-, 9-, 18-, and 30-month-old rats was examined. No major changes in SDS-PAGE protein profiles were noticeable. However, endogenous (auto) and exogenous phosphorylation in the presence of (gamma-32P)ATP showed an age-dependent increase in 32P uptake. pH optimum was between 8.0 and 9.0 for all age groups. Cyclic AMP was without effect on either endogenous or exogenous phosphorylation. Further analysis of the autophosphorylation reaction by quantification of autoradiograms obtained from SDS-PAGE gels displayed an age-dependent increase in phosphorylation of bands 2, 3, 4.1, and 4.5 [nomenclature of Fairbanks et al. Biochemistry 10:2606, 1971] and of several other minor bands. The data imply that alteration in red cell membranes may occur during aging of rats causing an enhancement in endogenous kinase activity and possibly in the number of phosphate acceptor sites as well.