ALTERATIONS IN THE PROTEINS OF SEA URCHIN EGG HOMOGENATES TREATED WITH CALCIUM

Abstract

Experiments are described whose purpose is the analysis, at the molecular level, of the "surface precipitation reaction" of living cells, and by extension, of the mechanism of the cyto-plasmic sol-gel transformation. The addition of Ca++ to homo-genates of Arbacia punctulata eggs (these having been freed, previously, of their ionic Ca) effects a solubility loss in a fraction of the cell''s proteins. The concentrations of the cation required together with the kinetics of the reaction suggest that the solubility loss involves the same pathway as do the surface precipitation reaction and the sol-gel transformation in the living cell. Proteolytic activity is evoked by the addition of Ca++, and non-protein nitrogen is released during incubation of the homogenates with the cation. The possible relation of this enzymatic activity to the aggregation phenomenon is discussed. Electrophoretic and electron microscopic investigations of the aggregation reactions in the homogenate lead to the hypothesis that the fraction which "clots" in the presence of Ca++ is distinct from the large granule group, is very rich in PNA, and consists of spherical macromolecules or particulates whose diameter is 350 to 400A. The submicroscopic morphology of the aggregates is described in relation to the probable course of events and aggregation pattern in the intact cell.