A single nucleotide polymorphism of CYP2B6 found in Japanese enhances catalytic activity by autoactivation

A single nucleotide polymorphism (SNP) resulting in a substitution from Gin to His was found in exon 4 of the CYP2B6 gene in Japanese. The frequency o f the variant allele was found to be 19.9%. The mutant- and the wild-type e nzymes were expressed in Escherichia coli, and the effects of the single am ino acid substitution on the catalytic activity were examined by investigat ing the kinetic profiles of 7-ethoxycoumarin O-deethylase activity. The wil d-type enzyme showed typical Michaelis-Menten kinetics, while the mutant-ty pe enzyme represented the sigmoidal kinetics with a higher V-max value comp ared to that of the wild-type enzyme. Eadie-Hofstee plots further revealed an existence of allosteric effects for the reaction catalyzed by the varian t. This is the first evidence demonstrating that only one amino acid substi tution, Gln172His, caused by natural SNP enhances the catalytic activity of CYP by obtaining the character of homotropic cooperativity. stool Academic Press.