?In vivo? ageing of human erythrocytes and cell-surface labeling by ?-galactose oxidase and sodium borotritide

Young and old, human erythrocytes, separated in vitro according to their age in vivo, were radioactively labeled at the cell-surface d-galactosyl and 2-acetamido-2-deoxy-d-galactosyl residues by treatment with d-galactose oxidase, followed by reduction with sodium borotritide. The labeling was quantitatively determined for each type of erythrocyte by measuring the molar amounts of borohydride necessary for the complete reduction of the oxidized residues. The number of surface residues per blood-group A+ erythrocyte was found to be 37.6 ± 1.8 × 106 (n  8) for young, 21.8 ± 4.9 x 106 (n  8) for old, and 24.8 ± 6.4 x 106 (n  8) for middle-aged erythrocytes, indicating a significant decrease of the residues during ageing.