title: Characterization of nucleoside triphosphatase activity in isolated pea nuclei and its photoreversible regulation by light.
abstract: A nucleoside triphosphatase (NTPase) present in highly purified preparations of pea nuclei was partially characterized.  The activity of this enzyme was stimulated by divalent cations (Mg2+ = Mn2+ > Ca2+), but was not affected by the monovalent cations, Na+ and K+.  The Mg(2+)-dependent activity was further stimulated by concentrations of Ca2+ in the low micromolar range.  It could catalyze the hydrolysis of ATP, GTP, UTP, and CTP, all with a pH optimum of 7.5.  The nuclear NTPase activity was not inhibited by vanadate, oligomycin, or nitrate, but was inhibited by relatively low concentrations of quercetin and the calmodulin inhibitor, compound 48/80.  The NTPase was stimulated more than 50% by red light, and this effect was reversed by subsequent irradiation with far-red light.  The photoreversibility of the stimulation indicated that the photoreceptor for this response was phytochrome, an important regulator of photomorphogenesis and gene expression in plants.
authors.affiliation: Department of Botany, University of Texas at Austin 78713, USA.
authors.forename: Y R
authors.initials: YR
authors.lastname: Chen
authors.forename: S J
authors.initials: SJ
authors.lastname: Roux
mesh_terms: D017766:Acid Anhydride Hydrolases / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000502:physiology; D002467:Cell Nucleus / Q000201:enzymology* / Q000502:physiology / Q000528:radiation effects; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007259:Infrared Rays; D008027:Light; D008274:Magnesium / Q000494:pharmacology* / Q000502:physiology; D008345:Manganese / Q000494:pharmacology; D043583:Nucleoside-Triphosphatase; D018532:Pisum sativum / Q000166:cytology / Q000201:enzymology* / Q000502:physiology / Q000528:radiation effects; D010834:Phytochrome / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology; D011794:Quercetin / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D003189:p-Methoxy-N-methylphenethylamine / Q000494:pharmacology
chemical_list: D002147:Calmodulin; D002614:Chelating Agents; D010834:Phytochrome; D003189:p-Methoxy-N-methylphenethylamine; D008345:Manganese; D004533:Egtazic Acid; D011794:Quercetin; D012964:Sodium; D017766:Acid Anhydride Hydrolases; D043583:Nucleoside-Triphosphatase; D008274:Magnesium; D011188:Potassium; D002118:Calcium