In the present study, we isolated modified LCAT (m-LCAT) by hydroxyapatite column chromatography after incubation of crude LCAT (after DEA SephadexA-50 column chromatography, penultimate step of LCAT purification) with oxidizedLDL (oxLDL) at 37degreesC for 1 h. The activity was found to be about 30% lower than that of native LCAT (n-LCAT). When activity was determined in the presence of oxLDL, m-LCAT was less inhibited than n-LCAT by oxLDL. Treatments of purified LCAT either at 56degreesC for 30 min, at 100degreesC for 10 min, or with 6 mM 5-5'-dithiobis-2-nitrobenzoic acid or 9 mM diisopropyl fluorophosphates (each at 37degreesC for 30 min) resulted in the loss of its cholesterol-esterifying activity. When examined for their ability to detoxify oxLDL,, native LCAT and LCAT treated at 56degreesC for 30 min were found to detoxify oxLDL. These results indicate that oxidation product(s) of LDL is transferred and bound to LCAT in a way that does not depend on its cholesterol-esterifying activity, but rather on the availability of the sulfhydryl group of cysteine residue and the hydroxyl group of serine residue. (C) 2002 Elsevier Science (USA).