STUDIES ON THE RIBONUCLEOPROTEIN PARTICLES

Abstract

The ribonucleoprotein particles were extracted from rat liver microsomes with a deoxycholate solution purified by precipitation at pH 4.2 and repeated centrifugation. The particles contained neither protease nor dipeptidase, but upon incubation at pH 7.0, 30-37[degree]C, there was a degradation of protein moiety and a marked release of RNA. This autodegradation cannot be prevented even by the addition of sucrose (0.25 [image]) or casein (0.125%). The optimum pH for autodegradation is pH 8.0. The particles exhibit alkaline ribo-huclease (RNAse) activity towards yeast RNA. This RNAse is fairly thermostable (up to 80[degree]C) and inhibited by the rat liver supernatant fluid (105,000 x G, 2 hours centrifugation). Since the RNAse activity per g of protein of the ribonucleoprotein particles is about twice as active as that of microsomes in spite of approximately the same RNA contents, the RNAse of the former is activated compared with RNAse in the latter. RNA molecules are bound to the protein moiety of the particles to stabilize the dispersion state.