Effect of ethanol on ratliver ribonucleoprotein previously exposed to cold trichloroacetic acid.

The separation of liver ribonucleic acid and deoxyribonucleic acid from the associated protein material without hydrolysis can be accomplished by a salt-extraction procedure described by Barnum & Huseby (1950). This method, based on ribose recovery (Lowe & Rand, 1956; C. U. Lowe & P. R. Venkataraman, in preparation), yields 80% of the total ribonucleic acid of normal liver homogenate or cell fractions. When ribonucleic acid was isolated by a salt-extraction procedure (described in the text) comparable with that of Tyner, Heidelberger & LePage (1953), which utilizes an initial treatment of the liver homogenate or cytoplasmic fraction with trichloroacetic acid followed by extraction with ethanol and ethanol-ether (3: 1, v/v), the yield, as measured by ultraviolet spectrophotometry and content of ribose and total phosphorus, was reduced to 62-53% of the total content. The apparent discrepancy between these two procedures was more obvious in the cytoplasmic fraction, and these observations motivated a detailed investigation to trace the possible source of loss of nucleic acid by the latter method. It was found that the first ethanol extract obtained after exposure of nucleoprotein to cold trichloroacetic acid contained appreciable amounts of ribonucleic acid-like material. If, after exposure of the nucleoprotein to cold trichloroacetic acid, ethanol treatment was omitted, extraction of the precipitated nucleoprotein with hot 10% sodium chloride solution, after neutralization of the excess of trichloroacetic acid, restored the yield of ribonucleic acid to a level of 80% of the total content. The results reported here appear to emphasize that ribonucleoprotein previously exposed to cold trichloroacetic acid is solubilized by ethanol even in the cold. In contrast, deoxyribonucleic acid protein appears to be unaffected.