The utilization of unesterified palmitate by Ehrlich ascites tumor cells.

Ehrlich ascites tumor cells have been shown to take up long chain free fatty acids from albumin-FFA’ complexes very rapidly in vitro. The uptake during the 1st min of exposure of the cells is dependent on the FFA-albumin molar ratio in the medium (I? 2). Most of the FFA initially taken up is present in unesterified form, and at least 50% of it is reversibly bound (2). The initial FFA uptake is not decreased significantly by addition of metabolic inhibitors to the incubation medium (2). These observations, coupled with those of Goodman on the binding of palmitate by erythrocyte membranes (3), suggest that the initial process in cellular FFA uptake is an energy-independent, reversible transfer of FFB from albumin to cell surface binding sites. The degree of saturation of the cellular fatty acid-binding sites at equilibrium is determined by the molar ratio of the FFA-albumin complex to which the cell is exposed, independent of the total FFA concentration (2, 3). The present studies were undertaken to determine the extent to which the FFA rapidly and reversibly taken up by the cells are available for esterification and oxidation. The results indicate that the bulk of this FFA fraction is utilized readily. By extended incubation of cells in the presence of albumin-FFA at different molar ratios, it is shown that the rate of oxidation and esterification of exogenous FFA is directly related to the extent to which the capacity of the cells to bind FFA is saturated, i.e. the relative “concentration” of FFA in relation to the total binding sites available.