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.
- © 1982 London: The Biochemical Society