title: Phosphorylation of purified Novikoff hepatoma topoisomerase I.
abstract: The purified Novikoff hepatoma nuclear phosphoprotein with a molecular weight of 110 kdalton and pI 8.4, was found to be a type I topoisomerase. When isolated from 32P-labeled Novikoff ascites cells or incubated in vitro with protein kinase, phosphoserine was found to be its major phosphorylated amino acid. The enzymatic activity of topoisomerase I was altered by changes in phosphorylation. Its activity was increased by protein kinase and it was decreased by alkaline phosphatase.
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D004264:DNA Topoisomerases, Type I / Q000302:isolation & purification* / Q000378:metabolism; D004789:Enzyme Activation; D008114:Liver Neoplasms, Experimental / Q000201:enzymology*; D009363:Neoplasm Proteins / Q000302:isolation & purification*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats
chemical_list: D009363:Neoplasm Proteins; D011494:Protein Kinases; D000469:Alkaline Phosphatase; D004264:DNA Topoisomerases, Type I