Studies on isolated cell components: XIII. The effect of heat on rat liver soluble proteins

Abstract

The precipitation of rat liver soluble proteins as a function of time and temperature has been studied in terms of total nitrogen precipitated and turbidity developed. At 40 °C ~ 10 per cent of the nitrogen precipitated in 2 hours; at 100 °C, 86 per cent was flocculated. The amount of precipitation diminished rapidly as the pH was raised from 6.4 to 8.2. The flocculation observed especially at lower temperatures (~ 40 °C) is not attributable to a decrease in pH during incubation. Evidence for a pH homeostatic mechanism was found. Addition of polyanions (ATP, RNA, heparin, polymanuronic acid sulfate) markedly decreased the rate of precipitate formation, but RNase, calcium chloride, and magnesium chloride promoted precipitation. It is suggested that in vivo precipitation is largely prevented by maintaining appropriate levels of ATP, RNA, and other polyanions. The relation of these findings to cytoplasmic structure and function and to intracellular viscosity changes is discussed.