[Polynucleotide phosphorylase from rat liver: isolation and regulation of its activity by growth hormone].

Using ion-filtration chromatography on DEAE-Sephadex A-25, a homogeneous polynucleotide phosphorylase having specific activity of 350--360 u./mg and containing no admixtures of nucleases or phosphatases was obtained. Injection of 32P phosphate to hypophysectomized animals was accompanied by the label incorporation into the enzyme molecule. The data obtained indirectly indicate that the enzyme is activated by phosphorylation and is inactivated by dephosphorylation, both processes being mediated by some factor found in liver cytosol of intact animals.