title: Purification and characterization of a cyclic nucleotide-regulated 5'-nucleotidase from potatoe.
abstract: A procedure is presented for the rapid purification of a 5'-nucleotidase (5'-ribonucleotide phosphohydrolase, EC 3.1.3.5) from potato tubers, involving ammonium sulphate fractionation and chromatography on phosphocellulose, DEAE-cellulose and Sephadex G-75. Application of this procedure results in a 6000-fold purification of the 5'-nucleotidase and the final preparations are virtually homogeneous, yielding only one protein band on electrophorsis in polyacrylamide gels in non-dissociating or dissociating conditions. The 5'-nucleotidase has a molecular weight of 50 000 from gel filtration experiments. Sodium dodecylsulphate-polyacrylamide gel electrophoresis of the purified 5'-nucleotidase reveals one major band of molecular weight 25 000. The 5'-nucleotidase is competitively inhibited by cyclic nucleotides, having micromolar Ki values for cyclic AMP and cyclic GMP at pH 5.0 and pH 8.0. The enzyme has a pH optimum of 5.0 with 5'-GMP as substrate. While 5'-AMP and 3'-AMP are hydrolyzed at comparable rates at pH 5.0, at pH 8.0 the rate of hydrolysis of 3'-AMP is only 4% of that with 5'-AMP. ADP, ATP and 2'-AMP are very poor substrates for the enzyme. The nucleotidase has micromolar Km values for nucleoside 5'-monophosphates other than 5'-NMP. A wide variety of divalent cations activate the 5'-nucleotidase.
mesh_terms: D002104:Cadmium / Q000494:pharmacology; D002413:Cations, Divalent; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D000242:Cyclic AMP / Q000494:pharmacology*; D006152:Cyclic GMP / Q000494:pharmacology*; D004355:Drug Stability; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000187:drug effects; D005459:Fluorides / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007854:Lead / Q000494:pharmacology; D008970:Molecular Weight; D009708:Nucleotidases / Q000302:isolation & purification / Q000378:metabolism*; D010944:Plants / Q000201:enzymology*; D013997:Time Factors
chemical_list: D002413:Cations, Divalent; D002104:Cadmium; D007854:Lead; D000242:Cyclic AMP; D009708:Nucleotidases; D006152:Cyclic GMP; D005459:Fluorides