[Polynucleotide phosphorylase from rat liver nuclei. Determination of the activity and some properties]

The activity of polynucleotide phosphorylase (PNPase) from rat liver nuclei isolated in aqueous and non-aqueous media was studied. It was shown that aqueous and non-aqueous nuclear preparations differ both in specific activity (106 and 39 units per mg of protein, respectively) and in the enzyme content (11.2 and 3.4% of homogenate activity, respectively). Nuclear PNPase reveals its maximal activity at pH 7.6-8.0 and requires Mg2+. The enzyme catalyzed polyribonucleotide phosphorelysis in the following order: poly (A) leads to poly(U) leads to poly(S) leads to RNA leads to poly(A) . poly(U). It is concluded that a comparatively low PNPase activity of the nuclei isolated in sucrose media is due to the enzyme extraction from the nuclei in the course of isolation.