title: Steady-state kinetic studies of the inhibitory action of Zn2+ on ribonuclease T1 catalysis.
abstract: The kinetic mechanism of specific inhibition by Zn2+ of ribonuclease T1 catalysis was studied by steady-state kinetic analysis of transphosphorylation of dinucleotides, GpCp(3'), GpUp(2') and GpUp(3'), and dinucleoside monophosphates, GpC and GpU. The inhibition was not simply competitive, non-competitive or uncompetitive, but the kinetic data were compatible with a mechanism of 'fully mixed inhibition' in which a fully non-competitive action was associated with a partially competitive action. Apparent equilibrium quotients involved in this model of inhibition were determined for the dinucleotide substrates, and we found that binding of either of Zn2+ and substrate was facilitated when the other was bound. The location of Zn2+ was suggested to be near His-40 and/or His-92 of the ribonuclease T1 molecule.
mesh_terms: D001665:Binding Sites; D015226:Dinucleoside Phosphates; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D046911:Macromolecular Substances; D008956:Models, Chemical; D009841:Oligonucleotides / Q000378:metabolism; D010766:Phosphorylation; D006163:Ribonuclease T1 / Q000037:antagonists & inhibitors*; D012260:Ribonucleases / Q000037:antagonists & inhibitors*; D015032:Zinc / Q000494:pharmacology*
chemical_list: D015226:Dinucleoside Phosphates; D046911:Macromolecular Substances; D009841:Oligonucleotides; D012260:Ribonucleases; D006163:Ribonuclease T1; D015032:Zinc