The flavin-containing monooxygenases (FMO / E.C.1.14.13.8) are microsomal NADPH and oxygen-dependent flavoprotein enzymes that catalyze the oxidation of a wide variety of xenobiotics, including drugs and environmental toxicants. Nucleophiles containing nitrogen, sulfur, phosphorus and selenium heteroatoms are the substrates of FMO.
Bovine liver microsomal FMO enzyme activity was characterized using methimazole as substrate, which is a highly specific substrate for FMO. From 12 different bovine liver samples, microsomes were prepared and the average specific activity of bovine liver microsomal FMO was found to be 2.37 & / #61617 / 0.30 nmol/min/mg (Mean & / #61617 / SE, n=12). The rate of reaction was linear up to 0.5 mg of bovine liver microsomal protein. The maximum FMO enzyme activity was detected at 37 & / #61616 / C and at pH 8.0. Effects of detergents / Triton X-100 and Emulgen 913, on FMO activity were determined and found that enzyme activity increased by the addition of either detergent at all concentrations (0.1%-1.0%). The apparent Vmax and Km values of bovine liver microsomal FMO for methimazole substrate were found as 1.23 nmol/min/mg and 0.11 mM, respectively.
Thermostability of bovine liver microsomal FMO was studied at four different temperatures / 24 & / #61616 / C, 37 & / #61616 / C, 50 & / #61616 / C and 65 & / #61616 / C. The incubation time required for the complete loss of enzyme activity was 5 minutes at 65 & / #61616 / C, 10 minutes at 50 & / #61616 / C and 6.5 hours at 37 & / #61616 / C. 68 % of the activity was still detectable at the end of 53 hours at 24 & / #61616 / C. Bovine liver microsomal activity towards two drug substrates, imipramine and chlorpromazine, was also determined and found to be 3.73 and 3.75 nmol NADPH oxidized/min/mg, respectively. Effects of two drug substrates, imipramine and chlorpromazine, on bovine liver microsomal FMO-catalyzed methimazole oxidation activity was also studied and found that they inhibit FMO activity at all concentrations studied.
Modulation of bovine liver microsomal FMO activity was studied using three different heavy metal ions / Ni+2, Cd+2 and Hg+2. At all other concentrations studied for each heavy metal ion and at all substrate methimazole concentrations (0.1, 0.2, 0.5, 1.0 mM), FMO-catalyzed methimazole oxidation activity decreased compared to control activity. KI values for Ni+2, Cd+2 and Hg+2 were found to be 0.5 mM, 0.085 mM, 4.6 & / #61549 / M, respectively. From the Dixon plot, the pattern of inhibition for three heavy metal ions was observed to be noncompetitive.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12604749/index.pdf |
| Date | 01 January 2004 |
| Creators | Baser, Deniz Fulya |
| Contributors | Adali, Orhan |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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