The metabolism of 2,5-diphenyloxazole (PPO) in human lymphocytes and rat liver microsomes.
The oxidative metabolism of 2,5-diphenyloxazole (PPO) is associated with 3-methylcholanthrene inducible cytochrome P-450. The major metabolite formed has m/z of 237, corresponding to hydroxylated PPO. All the possible hydroxylated metabolites of PPO were synthesized and characterized, enabling the assignment of a structure for the major metabolite and two minor metabolites. The metabolites are easily extracted and their fluorescence is quantifiable in alkaline medium with a sample fluorescence to blank fluorescence ratio of 400:1. A sensitive HPLC assay of PPO metabolism was also developed. PPO metabolism is readily catalyzed by 3-methylcholanthrene-induced rat liver microsomes and strongly inhibited by alpha-naphthoflavone, but poorly inhibited by metyrapone or SKF 525A, indicating the involvement of cytochrome P-448 or P1-450 in the metabolism of PPO. With human lymphocytes the method has proven to be a good indicator of "aryl hydrocarbon hydroxylase" (AHH) activity, correlating well with AHH assays using benzo(alpha)pyrene (BP) as a substrate. Both the induced BP and PPO metabolism by human lymphocytes is inhibited by alpha-naphthoflavone, but not by metyrapone.
Department of Applied Biology, Royal Melbourne Institute of Technology, Vic, Australia.
J T
JT
Ahokas
C
C
Davies
N
N
Jacobsen
N T
NT
Kärki
A
A
Philippides
A M
AM
Treston
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002849:Chromatography, Gas; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D006801:Humans; D008214:Lymphocytes / Q000378:metabolism*; D008297:Male; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000378:metabolism*; D010080:Oxazoles / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet
D010080:Oxazoles; C009012:2,5-diphenyloxazole; D001189:Aryl Hydrocarbon Hydroxylases