COOXIDATIVE METABOLISM OF 4-AMINOBIPHENYL BY LIPOXYGENASE FROM SOYBEAN AND HUMAN TERM PLACENTA

)4-aminobiphenyl (4-ABP) co-oxidation catalyzed by the human term plac ental lipoxygenase (HTPLO), purified by affinity chromatography, was s tudied in the presence of linoleic acid (LA), Soybean lipoxygenase (SL O) which is extensively employed as a model lipoxygenase, was used for comparison. Spectral analyses of reaction media containing 4-ABP, LA, and SLC/HTPLO suggested the disappearance of substrate (Delta A at 27 0 nm) and a gradual appearance of a new peak at 315 nm, indicating a m etabolite formation. Under optimal assay conditions, SLC exhibited a s pecific activity of 350 nmoles of CABP depleted/min/nmole of enzyme. T o observe the maximal rate of co-oxidation by the HTPLO (45 nmoles of 4-ABP depleted/min/mg protein), an incubation of 50 mu M 4-ABP, 2 mM L A, and 80 mu g/ml protein at pH 7.4 was essential, 4-ABP was also oxid ized by SLO in the presence of H2O2, although at a lower rate, The rev ersed-phase HPLC analysis of organic extracts of the incubations of 4- ABP with SLO and H2O2/LA as well as HTPLO and LA showed the formation of a major peak which was identified by CC-MS as 4,4'-azobis(biphenyl) . The addition of GSH, BHT, and BHA to the enzymatic incubations decre ased the formation of 4-ABP metabolite, suggesting the generation of a free radical as the initial metabolite during 4-ABP oxidation, Both t he SLO and HTPLO mediated reactions were significantly inhibited by no rdihydroguaiaretic acid, gossypol, and 5,8,11-eicosatriynoic acid, Col lectively, these results suggest that the co-oxidation catalyzed by HT PLO may be the underlying biochemical mechanism responsible for the tr ansplacental toxicity of 4-ABP.