Milieu-induced, selective aggregation of regulated secretory proteins in the trans-Golgi network

The percentage of PIS]sulfate-labeled SgII found in the pellet after incubation of [3'S]sulfate-labeled TGN vesicles in either nonaggregative or aggregative milieu in the presence of Triton X-100 was determined in four different experiments (Table I) Optical density values were integrated, and the total (pellet plus supernatant) [35S]sulfate-labeled SgII at each calcium concentration and pH was calculated . For each pH, the mean of these total values was calculated, and the total values obtained at the individual calcium concentrations, which differed from the mean by 420%, were then normalized to the mean. The integrated optical density values for SgII in the pellet after normalization are given as arbitrary units. For pH 6.9, the results of a single experiment are shown. For pH 6.4 and pH 7.4, the mean ofduplicate experiments, normalized to the maximum value (pH 6.4, 10mM calcium; pH 7.4, 20 mM calcium) is shown; bars indicate the variation of the single values from the mean.