TY - JOUR T1 - Co-oxidative Metabolism of 4-Aminobiphenyl by Lipoxygenase from Soybean and Human Term Placenta JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 196 LP - 105 VL - 25 IS - 2 AU - Kaushik Datta AU - Paul M. Sherblom AU - Arun P. Kulkarni Y1 - 1997/02/01 UR - http://dmd.aspetjournals.org/content/25/2/196.abstract N2 - }4-aminobiphenyl (4-ABP) co-oxidation catalyzed by the human term placental lipoxygenase (HTPLO), purified by affinity chromatography, was studied in the presence of linoleic acid (LA). Soybean lipoxygenase (SLO) which is extensively employed as a model lipoxygenase, was used for comparison. Spectral analyses of reaction media containing 4-ABP, LA, and SLO/HTPLO suggested the disappearance of substrate (ΔA at 270 nm) and a gradual appearance of a new peak at 315 nm, indicating a metabolite formation. Under optimal assay conditions, SLO exhibited a specific activity of 350 nmoles of 4-ABP depleted/min/nmole of enzyme. To observe the maximal rate of co-oxidation by the HTPLO (45 nmoles of 4-ABP depleted/min/mg protein), an incubation of 50 μM 4-ABP, 2 mM LA, and 80 μg/ml protein at pH 7.4 was essential. 4-ABP was also oxidized by SLO in the presence of H2O2, although at a lower rate. The reversed-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 GC-MS as 4,4′-azobis(biphenyl). The addition of GSH, BHT, and BHA to the enzymatic incubations decreased the formation of 4-ABP metabolite, suggesting the generation of a free radical as the initial metabolite during 4-ABP oxidation. Both the SLO and HTPLO mediated reactions were significantly inhibited by nordihydroguaiaretic acid, gossypol, and 5,8,11-eicosatriynoic acid. Collectively, these results suggest that the co-oxidation catalyzed by HTPLO may be the underlying biochemical mechanism responsible for the transplacental toxicity of 4-ABP. The American Society for Pharmacology and Experimental Therapeutics ER -