Publications

• The pyridine nucleotide cycle: presence of a nicotinamide mononucleotide-specific glycohydrolase in Escherichia coli.

  Andreoli A.J., Okita T.W., Bloom R., Grover T.A.

  Biochem Biophys Res Commun 49:264-269(1972) [PubMed] [EuropePMC]

• Isolation and properties of a glycohydrolase specific for nicotinamide mononucleotide from Azotobacter vinelandii.

  Imai T.

  A glycohydrolase that catalyzes the irreversible conversion of NMN to nicotinamide and ribose 5-phosphate has been partially purified from a sonic extract of Azotobacter vinelandii. The enzyme is highly specific for NMN. NAD, NADP, nicotinic acid-adenine dinucleotide, nicotinamide riboside and alp ... >> More

  A glycohydrolase that catalyzes the irreversible conversion of NMN to nicotinamide and ribose 5-phosphate has been partially purified from a sonic extract of Azotobacter vinelandii. The enzyme is highly specific for NMN. NAD, NADP, nicotinic acid-adenine dinucleotide, nicotinamide riboside and alpha-NMN are not significantly hydrolyzed by this enzyme, nor do they compete with NMN. The enzyme also exhibits an absolute dependence on guanylic acid derivatives with following order of relative effectiveness: GTP, guanosine 5'-tetraphosphate greater than dGTP, GDP, 2'-GMP, 3'-GMP greater than GMP, dGMP. A heat-resistant, nondialyzable factor which could replace the GTP requirement was found in the sonic extract. The Ka for GTP and the Km for NMN in the presence of GTP at 1mm were calculated to be 0.025 mM and 4.5 mM respectively. GMP, dGMP, and dCMP were found to be effective inhibitors of the enzyme when 1 mM GTP was also present. The kinetic data suggest that the binding site for these mononucleotides is distinct from the active site or the GTP binding site. The ability of this enzyme to cleave NMN is suggestive of a metabolic role of the enzyme in selective conversion of NMN to nicotinamide, which, in turn, would be re-utilized by the cell as a precursor of NAD via nicotinic acid. << Less

  J Biochem 85:887-899(1979) [PubMed] [EuropePMC]

• Properties of allosteric nicotinamide mononucleotide glycohydrolase from Azotobacter vinelandii: activation and inhibition.

  Imai T.

  In order to clarify the regulation mechanism of NMN glycohydrolase, a number of purine and pyrimidine nucleotides were tested as activators for the enzyme. Among naturally occurring nucleotides, pppGpp was shown to be the most potent activator (KA = 0.0087 mM). The effectiveness of these nucleotid ... >> More

  In order to clarify the regulation mechanism of NMN glycohydrolase, a number of purine and pyrimidine nucleotides were tested as activators for the enzyme. Among naturally occurring nucleotides, pppGpp was shown to be the most potent activator (KA = 0.0087 mM). The effectiveness of these nucleotides estimated from Vmax/KA was in the order: pppGpp greater than ppGpp greater than pppppG greater than ppppG greater than pGpp greater than GTP greater than or equal to 2'-GMP greater than or equal to GppppG greater than dGTP greater than ITP greater than GDP = 2'-O-methylGTP. XTP, UTP, dTTP gave no effect. In contrast, ATP, CTP, and 7-methylGTP were inhibitory. A comparison of the data indicated that activation of the enzyme is specific for the base structure, guanine, and that effectiveness of nucleotides as activators results from the negatively charged phosphate moiety. Consistent with these results, inorganic polyphosphates (tri-, tetra-, and pentaphosphate) and 5-phosphoribose 1-pyrophosphate were shown to function as inhibitors of the enzyme. The inhibition mechanism was shown to be competitive with GTP. However, apparent Ki values for these inhibitors were dependent on the activator concentration. Furthermore, a shift of cooperativity type and progressive increase of positive cooperativity concomitant with increase of PRPP concentration were observed. These results indicate that this enzyme may be allosteric and an important regulatory component of pyridine nucleotide cycle metabolism. << Less

  J Biochem 101:163-173(1987) [PubMed] [EuropePMC]