[Paracatalytic interaction of pyruvate decarboxylase with quinones in the presence of an organic solvent. Formation of an active site which hinders proton transfer].

Inactivation kinetics of pyruvate decarboxylase under joint action of substrate and substituted quinones in aqueous solutions which contain 1.0-13.5 vol.% of methyl alcohol has been investigated. The observed inactivation rate constant of pyruvate decarboxylase sharply decreases with the increase of methanol concentration from 4 up to 7 vol.% at pH 5.8-6.4. The decrease of the rate constant is independent of quinone order in the kinetic inactivation equation. The result is that the decrease of microscopic dielectric permeability by interaction of methanol with hydrophobic cities of enzyme active surface hinders the transfer of proton at the stage which is limiting in the inactivation process. It is assumed that the organization of active centre of pyruvate decarboxylase may depend on hydrophobic contact.