The Uptake of [ l-3H]Glucosamine and Sodium I3’S]Sulphate into Glycoproteins Secreted by Mucus Glands of the Common Sea Mussel Mytilus edulis

Florisil (activated magnesium silicate) (Saito & Hakomori, 1971 ) or silicic acid (Vance & Sweeley, 1967). The glycolipids recovered from the membranes of unfractionated erythrocytes accounted for 33 %of the galactosamine, 6 % of the glucosamine, but less than 2 of the sialic acid of erythrocyte membranes. When erythrocyte populations from single individuals were fractionated on the basis of density differences it was observed that there was marked heterogeneity in membrane carbohydrate content. The oldest (most dense) cell fractions contained substantially smaller amounts of sialic acid, galactosamine, glucosamine, galactose and glucose when compared with younger cells (Table 1). The decrease in sialic acid content on cell aging must be mainly attributable to changes in cell-surface glycoprotein, because there is insufficient sialic acid in the glycolipid to account for a change of this magnitude. However, the suggestion that there may also be loss of glycolipid carbohydrate is supported by the observation that less hexosamine was obtained in the glycolipid fractions from the membranes of aged cells than from young cells. The population of circulating erythrocytes appears to be heterogeneous in both glycoprotein and glycolipid components, loss of carbohydrates contained in both types of molecule being associated with aging in uiuo.