title: Particulate-associated protein phosphatases of rat hepatomas as compared with the enzymes of rat liver.
abstract: In the course of investigating the neoplastic alterations of protein phosphatases, the particulate fractions of rat liver and AH-13, a strain of rat ascites hepatoma, were chromatographed on DEAE-cellulose and assayed for protein phosphatase using glycogen synthase D and phosphorylase a as substrates. The synthase phosphatase activity of rapidly growing AH-13 was due almost entirely to a divalent cation-inhibited protein phosphatase, tentatively designated phosphatase N, the level of which was elevated remarkably in the hepatoma as compared with liver. Other hepatomas including primary hepatoma induced with 3'-methyl-4-dimethylaminoazobenzene also exhibited high levels of this phosphatase. Phosphatase N exhibited Mr = 49,000 (gel filtration) and has been partially purified with little alteration in properties. Partially purified phosphatase N was inhibited by divalent cations, rabbit skeletal muscle polypeptide inhibitor-2 and heparin, and released the catalytic subunit of type-1 protein phosphatase upon tryptic digestion. It is therefore apparent that phosphatase N is a type-1 protein phosphatase. There is some evidence to suggest that the high levels of phosphatase N in neoplastic cells are due primarily to enhanced synthesis of its non-catalytic (regulatory) subunit.
authors.affiliation: Biochemistry Laboratory, Tohoku University, Sendai.
authors.forename: R
authors.initials: R
authors.lastname: Shineha
authors.forename: K
authors.initials: K
authors.lastname: Kikuchi
authors.forename: S
authors.initials: S
authors.lastname: Tamura
authors.forename: A
authors.initials: A
authors.lastname: Hiraga
authors.forename: Y
authors.initials: Y
authors.lastname: Suzuki
authors.forename: S
authors.initials: S
authors.lastname: Tsuiki
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D006007:Glycogen-Synthase-D Phosphatase / Q000032:analysis; D008099:Liver / Q000201:enzymology*; D008114:Liver Neoplasms, Experimental / Q000201:enzymology*; D008297:Male; D008970:Molecular Weight; D010749:Phosphoprotein Phosphatases / Q000032:analysis* / Q000037:antagonists & inhibitors / Q000302:isolation & purification; D051381:Rats
chemical_list: D000255:Adenosine Triphosphate; D010749:Phosphoprotein Phosphatases; D006007:Glycogen-Synthase-D Phosphatase