Co-oxidative metabolism of 4-aminobiphenyl by lipoxygenase from soybean and human term placenta.
]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 (deltaA 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 microM 4-ABP, 2 mM LA, and 80 microg/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.
Datta
K
K
Department of Environmental and Occupational Health, College of Public Health, University of South Florida, Tampa 33612-3805, USA.
Sherblom
P M
PM
Kulkarni
A P
AP
D000611:Aminobiphenyl Compounds / Q000378:metabolism*; D000975:Antioxidants; D002273:Carcinogens / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated; D005260:Female; D006801:Humans; D008084:Lipoxygenase / Q000302:isolation & purification / Q000378:metabolism*; D016859:Lipoxygenase Inhibitors / Q000494:pharmacology; D013058:Mass Spectrometry; D010084:Oxidation-Reduction; D010920:Placenta / Q000201:enzymology; D011247:Pregnancy; D013025:Glycine max / Q000201:enzymology; D013056:Spectrophotometry, Ultraviolet
D000611:Aminobiphenyl Compounds; D000975:Antioxidants; D002273:Carcinogens; D005231:Fatty Acids, Unsaturated; D016859:Lipoxygenase Inhibitors; C006757:4-biphenylamine; D008084:Lipoxygenase