SIALIC ACIDS ON THE PLASMA MEMBRANE OF CULTURED HUMAN LYMPHOID CELLS : Chemical Aspects and Biosynthesis

From 61 to 92% of the total sialic acid of a variety of human lymphoid cell lines maintained in tissue culture is present on the cell surface as measured by its susceptibility to cleavage by Clostridium perfringens neuraminidase. These cells contain from 1.22 x 10⁸ to 6.99 x 10⁸ molecules of surface sialic acid per cell. In synchronized cultures synthesis of surface sialic acid occurs only during a limited time in the late G₂ phase of the cell cycle. The amount and density of surface sialic acid vary considerably throughout the cell cycle.