Hydroperoxidase activity of lipoxygenase in the presence of cyclodextrins

The oxidation of xenobiotics by the hydroperoxidase activity of lipoxygenas e in the presence of cyclodextrins was studied. These produced an inhibitor y effect on xenobiotics oxidation, based on their degree of hydrophobicity and the charge (isoproterenol < 4-methyl-catechhol (4MC) < 4-tert-butylcate chol (TBC) < 4-tert-octylcatechol (TOC)). This inhibitory effect was due to the complexation of xenobiotics in the hydro phobic cavity of cyclodextrin s. The complexation constant K-c was calculated by nonlinear regression of the inhibition curves obtained in the presence of cyclodextrins, and the va lues obtained were 400, 16,250, and 35,127 M-1 for 4MC, TBC, and TOC, respe ctively. The validity of these values was checked at different points of th e Michaelis-Menten saturation curve, and a sigmoidal inhibition curve was o btained at the saturating concentration of the o-diphenol, TBC, with no cha nge in the K-c value. This demonstrates the validity of the equations used to calculate K-c for the complete range of the Michaelis-Menten equation. ( C) 1999 Academic Press.