| Abstract: | Lysosomal hydrolases are continually secreted by Acanthamoeba as a consequence of membrane cycling between the vacuolar compartment and the cell surface. In pinocytosing amoebae acid hydrolases can be separated into two groups on the basis of their secretion kinetics. We have previously shown that in Acanthamoeba acid hydrolases are almost exclusively restricted to a single compartment, digestive vacuoles, and that pH-dependent differential binding of hydrolases to vacuolar membrane can account for the different rates of hydrolase secretion from this compartment. In this report we show that the hydrolase secretion pattern changes and that all of the hydrolases are released with the same kinetics after phagocytosis of yeast or in growth media supplemented with ammonium acetate or chloroquine, but not after phagocytosis of polystyrene beads. The changes in the pattern of hydrolase secretion correlate with changes in vacuolar pH. The vacuolar pH of pinocytosing amoebae and amoebae saturated with beads is about 4.8. This value is increased to 6.8 by accumulation of weak bases and to about 6.1 when digestive vacuoles are saturated with yeast. These results indicate that vacuolar pH modulates hydrolase transport and secretion. |
