THE UPTAKE OF FLUORESCENT ALBUMIN BY PINOCYTOSIS IN Amoeba proteus

Holter and Marshall (7) demonstrated the uptake of fluorescein-labelled globulin by pinocytosis in the large ameba Chaos chaos (Pelomyxa carolinensls) and followed the fate of the ingested material in the cell by measurement of fluorescence and by observations on centrifuged amebae; their uptake experiments were made at pH 6.8. Brandt (1), also using fluorescein-labelled globulin at a similar pH, in the same species, showed that the plasmalemma and the walls of the pinocytotic vacuoles adsorbed the protein; he confirmed these results with specific antibody tests. Marshall, Schumaker, and Brandt (11) have discussed the importance of binding of protein to the surface of cells engaged in pinocytosis. A review by Holter (9) summarizes recent advances in this field. That many different types of protein induce pinocytosis has been shown by Chapman-Andresen and Prescott (5), and the effect of the pH of albumin solutions on the intensity of pinocytosis in Amoeba proteus, as determined by the number of channels observed, has been demonstrated by Chapman-Andresen (3); in aqueous solutions of bovine plasma albumin, pinocytosis is very intense at pH 4.1 to 4.8, while at pH 5.5 or above, it is completely absent. It was thought worthwhile to check the effects of pH on pinocytosis in amebae using fluoresceinlabelled albumin. The amoebae were immersed in fluorescent protein solutions at acid and at neutral pH, and by employing different conditions for washing the amebae after removal from the fluorescent protein solution, attempts were made to investigate the conditions for the binding of the protein to plasmalemma. The experiments reported here were designed to explore these possibilities in a qualititive manner; quantitative experiments involving counting of pinocytosis channels and measurements of fluorescence in groups of amebae have been planned and are in progress.