Oxidation of membrane proteins and functional activity of band 3 in human red cell senescence

The state of oxidation of membrane proteins was analyzed in red cell subpopulations of different age by quantifying the oxidation of methionine to its sulfoxide and by determining the amount of thiol groups in ghost membrane preparations and the reactivity of thiols of individual membrane proteins in intact cells. The results obtained show that oxidation of methionine occurs early during red cell life in the circulation, and can be detected in middle-aged and senescent cells. Thiol content of ghost membranes is kept constant in all the red cell subpopulations analyzed, but reactivity of thiol groups to the thiol reagent N-(7-dimethyl-amino-4-methyl-coumarinyl) maleimide (DACM) in intact cells decreased 30% in alpha-spectrin, band 3 (B3), 4.1 and 4.2 proteins, probably as a consequence of conformational changes of these molecules. Since the role played by band 3 in the exposure of senescence antigen has been described by many authors, the functional activity of the anion transporter has been analyzed by measuring the 4-4'-diisothiocyano-stilbene-2-2-'-disulfonate (DIDS) binding capacity in different red cell subpopulations. The results obtained are in agreement with the possibility that during senescence band 3 undergoes conformational changes involving the anion channel subsite being more exposed to the extracellular space and responsible for binding of DIDS.