Red cell membrane proteins in insulin-dependent diabetes: differential effects of treatment with calcium and various proteases.

Red cell ghosts prepared in the presence and absence of calcium from diabetics and age- and sex-matched controls, were subjected to proteolytic digestion with trypsin directly after extraction of the membranes and under conditions designed to maximize absorption of the protease to the membranes. Membranes were also directly digested with alpha-chymotrypsin and the V8 protease from S. aureus. The membrane protein profile was examined using sodium dodecyl sulfate (SDS) electrophoresis. In the untreated membranes, consistent apparent increases were seen in several minor bands in the area between bands 2 and 3 and in the area between the 4.1, 4.2 doublet and band 5. Calcium lysis caused major alterations in both diabetic and control membrane proteins. Trypsin hydrolysis proved most effective when the protease was preabsorbed to the membranes but whether preabsorbed or added directly prior to incubation, proteolysis was much less marked with the diabetic membranes. Only minor differences were seen in the alpha-chymotrypsin cleavage patterns and no differences at all were seen in the V8 protease cleavage patterns.