Changes in the proteolytic activity of human erythrocyte membrane during red cell aging

The action of endogenous membrane proteinases in membranes isolated from human red cells of various ages was assayed by three groups of methods: (1) determination of the amount of protein fragments released to the acid-soluble fraction; (2) monitoring of changes in ESR spectra of maleimide spin-labeled erythrocyte membranes; (3) electrophoretic methods; a two-dimensional analysis and analysis of the activity inside SDS-PAGE gels. For all the methods the effects of proteinase action were highest in ghosts isolated from the erythrocytes of middle age.