Configuration Change of Surface Sialic Acid during Mitosis

Changes in the metabolic state of a cell that permit (and perhaps trigger) mitosis are suggested from a variety of observations (see general discussions of the premitotic state: references 5, 7, 13). A list of such premonitory indications of mitosis should probably include increase in nuclear volume, loss of cellular water, cortical and endoplasmic viscosity changes partly or wholly related to calcium shifts, transient availability of protein sulfhydryl groups, as well as some sort of filling of an energy store. With mammalian cells, increased cell electro-phoretic mobility has been repeatedly associated with cell division (3, 6, 11, 17). Mayhew (12) has recently shown that in parasynchronous cultures of human osteosarcoma cells (RPMI No. 41) the transient elevation of mean cell electrophoretic mobility occurring just before, and during the division wave is related to neuraminidase-susceptible groups on the cell surface. Since electrophoretic mobility is a function of surface charge density (rather than total charge) and since surface sialic acid is well known as a participant in electropho-retie mobility of many kinds of cells (1, 2, 4, 21), Mayhew's observations raise an interesting question (discussed in some detail in his paper, as well as in a recent paper by Weiss, 24): does the transient charge density elevation indicate a transient elevation of the density of surface sialic acid molecules , or does it, instead, relate to a change in the spatial or charge exposure relationship of the same molecules to the electrokinetic shear layer? Previous work in this laboratory (8) indiciated that changes in total sialic acid per cell were associated with changes in mean cell volume when parasynchronous Chinese hamster ovary (CHO) cells were followed through a division wave. Assays of randomly growing cells showed that two-thirds of the total sialic acid was located on the cell surface, one-third being bound to intracellular molecules. These conclusions were reached on the basis of Warren assays (23) of materials released from either intact cells or broken cells by means of neuraminidase treatment or mild acid hydroly-sis. It was conceivable, therefore, that electro-phoretic mobility changes related to cell division might involve fluctuations of intracellular and surface sialic acid even though the shift was probably too rapid to invoke a mechanism involving synthesis de novo and release (9, 18). The present report deals with measurement of surface sialic acid as a function of cell surface area in parasyn-chronous CHO cells released from thymidine block (15). …