The relation between intracellular pH and rate of protein synthesis in sea urchin eggs and the existence of a pH-independent event triggered by ammonia

Abstract

The relation between rate of protein synthesis and intracellular pH (pH i ) was investigated in the eggs of the sea urchin Strongylocentrotus purpuratus. Increasing external pH (pH o ) resulted in raising pH i of eggs and also in increased rate of protein synthesis. Similarly, at constant pH o , adding various concentrations of NH 4Cl to eggs caused graded increases of both pH i and protein synthesis. Using various concentrations of NH 4Cl at a low pH o and incubating eggs at high pH o , we compared protein synthesis under similar pH i conditions and this revealed that at least half the increased protein synthesis stimulated by NH 4Cl is independent of induced rise of pH i , as also seems to be chromosome condensation which was never observed in eggs incubated at high pH o s. The additional pH-independent event triggered by NH 4Cl does not appear related to elevated free Ca 2+, since protein synthesis and chromosome condensation do not require external Ca 2+ and no increases of free Ca 2+ sufficient to activate the Ca 2+-calmodulin-mediated enzyme NAD kinase occurred. Monensin disrupts intravesicular pH gradients but does not stimulate protein synthesis, indicating that this local effect, also promoted by NH 4Cl, is not involved in ammonia-induced increase of protein synthesis. Using two other amines which have low pK a values, benzocaine and tricaine, we observed 2-fold increases in protein synthesis rates, even though pH i was lowered. While the exact nature of the pH-independent event(s) triggered by NH 4Cl, and possibly by other amines, remains unidentified, its possible involvement in normal mitosis is stressed.