title: The requirement for bivalent cations in formation of nicotinamide-adenine dinucleotide by nicotinamide mononucleotide adenylyltransferase of pig-liver nuclei.
abstract: 1. The requirement for bivalent cations in catalysis of NAD formation from ATP and NMN in the presence of NMN adenylyltransferase of pig-liver nuclei was studied. Rates of NAD formation in the presence of the activating cations Cd(2+), Mn(2+), Mg(2+), Zn(2+), Co(2+) and Ni(2+) were approximately a linear function of heats of hydration of the corresponding ions. Ba(2+), Sr(2+), Ca(2+), Cu(2+) and Be(2+) did not activate the enzyme; Be(2+) inhibited the reaction in the presence of Mg(2+) and, to a greater extent, in the presence of Ni(2+). 2. Michaelis constants for NAD formation, measured in a coupled assay with NMN adenylyltransferase and alcohol dehydrogenase at pH8.0 and 25 degrees , in the presence of 3mm concentrations of the unvaried reactants, were 88+/-7mum-ATP, 42+/-4mum-NMN and 85+/-4mum-Mg(2+). The results at this pH and at pH7.5 were consistent with mechanisms in which Mg(2+)-ATP complex is a reactant and free ATP a competitive inhibitor. 3. Formation of nicotinamide-hypoxanthine dinucleotide from NMN and ITP in the presence of the transferase was also more rapid with Ni(2+) and Co(2+) than with Mg(2+).
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001608:Beryllium; D002104:Cadmium; D002467:Cell Nucleus / Q000201:enzymology*; D003035:Cobalt; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000201:enzymology*; D008274:Magnesium; D008345:Manganese; D009243:NAD / Q000096:biosynthesis*; D009532:Nickel; D009713:Nucleotidyltransferases / Q000378:metabolism*; D013552:Swine; D015032:Zinc
chemical_list: D002104:Cadmium; D009243:NAD; D003035:Cobalt; D008345:Manganese; D009532:Nickel; D000255:Adenosine Triphosphate; D009713:Nucleotidyltransferases; D008274:Magnesium; D015032:Zinc; D001608:Beryllium