Characterization of a common genetic defect of cytochrome P-450 function (debrisoquine-sparteine type polymorphism)--increased Michaelis is Constant (Km) and loss of stereoselectivity of bufuralol 1'-hydroxylation in poor metabolizers

Biochem Biophys Res Commun. 1984 Nov 30;125(1):374-80. doi: 10.1016/s0006-291x(84)80378-2.

Abstract

In order to define the mechanism of the debrisoquine-sparteine type genetic polymorphism of drug oxidation we studied the kinetics of bufuralol 1'-hydroxylation in liver microsomes from extensive and poor metabolizers and in a purified reconstituted human cytochrome P-450 isozyme with high activity for bufuralol 1'-hydroxylation, P-450[buf]. In extensive metabolizer microsomes the enzymatic reaction displayed apparent Michaelis-Menten kinetics and the (+)-isomer was preferentially metabolized. By contrast, the enzymatic reaction in poor metabolizer microsomes was characterized by a 4- to 5-fold increase in Km and by a loss of stereoselectivity. In a non-membraneous reconstituted system containing NADPH cytochrome P-450 reductase, a NADPH regenerating system and phospholipids, P-450[buf] exhibited an almost complete substrate stereoselectivity for (+)-isomer 1'-hydroxylation. It is concluded that the purified cytochrome P-450[buf] is the target of the debrisoquine-sparteine type oxidation polymorphism and that poor metabolizers have a quantitative or qualitative deficiency of this isozyme.

MeSH terms

  • Cytochrome P-450 Enzyme System / genetics*
  • Cytochrome P-450 Enzyme System / metabolism
  • Ethanolamines / metabolism*
  • Humans
  • Isoenzymes / metabolism
  • Kinetics
  • Microsomes, Liver / enzymology
  • Polymorphism, Genetic*
  • Stereoisomerism

Substances

  • Ethanolamines
  • Isoenzymes
  • bufuralol
  • Cytochrome P-450 Enzyme System