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.