Phosphorus compounds in the cell. 1. Protein-bound phosphorus fractions studied with the aid of radioactive phosphorus

Abstract

The Schmidt-Thannhauser and the Schneider separation procedures were applied to tissues, chiefly liver, from rats and rabbits injd. with P . The specific activities of the fractions containing the nucleic acids were invariably considerably higher than those of the nucleic acids isolated from the same tissues. The "phosphoprotein P" set free from protein by incubation with alkali, invariably had a high specific activity. As detd. by the Schneider procedure it was always much larger in amt. but lower in activity than as obtained by the Schmidt-Thannhauser procedure, owing to the presence of other P compounds in the Schneider residue. Exhaustive extraction with ice-cold 10% trichloroacetic acid [TCA] fails to remove "phosphoprotein P" from liver tissue or to reduce its high specific activity. On the other hand, the high activity of this fraction may be due partly to persistent traces of acid-soluble phosphate, since P32 added as inorganic phosphate to a tissue homogenate was not completely, removed even by numerous washings with 10% TCA. Washing with TCA containing carrier phosphate was also inadequate. It is unjustifiable to assume that the specific activities of the nucleic acid fractions obtained by the Schmidt-Thannhauser procedure represent the true activities of the nucleic acids. In all expts. on protein-bound P fraction involving the use of P32 it is essential to eliminate the possibility of contaminating inorganic phosphate. To do this it is desirable to isolate the compounds under investigation in the pure state.