Kefal karaciğer mikrozomunda sitokrom P450'ye bağlı aldrin epoksidasyonunun karakterizasyonu

Organochlorine pesticides (OCPs) are lipid soluble chemicals and tend to accumulate in living organisms. The studies concerning the OCP measurements in living organisms are limited in the Black Sea. In this study, flathead mullet samples (Mugil cephalus) were caught from five different locations of the West Black Sea Region of Turkey in 2009. Organochlorine pesticides were extracted from the liver tissues and then the levels of OCPs were measured by using gas chromatography and electron capture detector. Organochlorine pesticides were detected in all locations. This result clearly indicated the presence of OCPs in the West Black Sea region of Turkey and exposure of living organisms to these chemicals. Bioaccumulation of chemicals in living organisms depends on the relative amounts and activities of the different biotransformation enzymes. In the present study, the metabolism of aldrin to its toxic metabolite dieldrin was studied in mullet liver microsomes. Fish liver microsomes were prepared by differential centrifugation. Aldrin epoxidase activitywas determined by measuring the amount of dieldrin produced using gas chromatography and electron capture detector in the liver microsomes. Maximal fish liver aldrin epoxidase activity was observed at pH 7.6 and protein concentration of 5 mg in 0.5 mL reaction mixture. Aldrin epoxidase exhibited monophasic kinetics with apparent Km value of 140 ?M for aldrin. Aldrin epoxidase activities of the samples caught from five different locations of the West Black Sea Region of Turkey were measured at the optimum conditions. The lowest aldrin epoxidase activity was measured in the mullets caught from Amasra. Mullets caught from Zonguldak Harbour, Sakarya River and Gülüç Stream Mouths displayed 2 fold higher aldrin epoxidase activities than Amasra. In addition, the contribution of cytochrome P450 isozyme(s) was determined by using specific cytochrome P450 inhibitors and substrates. Ketoconazole (CYP3A inhibitor), SKF-525A (CYP3A and CYP2B inhibitors) and cimetidine (CYP3A, CYP2C, CYP2D and CYP1A inhibitors) potentially inhibited the metabolism of aldrin, alpha-naphthoflavone (CYP1A inhibitor), tolbutamide (CYP2C substrate), diclofenac (CYP2C inhibitor), orfenadrine (CYP2B6 inhibitor), quinidine (CYP2D inhibitor) and aniline (CYP2E substrate) did not show inhibition. The results of this study suggest that CYP3A is the cytochrome P450 isozyme involved in aldrin epoxidation in mullet liver microsomes whereas CYP1A, CYP2C, CYP2D, CYP2B and CYP2E are not involved. Finally, the effects of Cu2+, Cr3+, Ni2+, Tl3+, Co3+, Mg2+ and Mn2+ on aldrin epoxidase activity were determined. Copper, thallium, nickel and chromium caused 95%, 22%, 15% and 13% inhibition on aldrin epoxidase activity, respectively.