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Lung microsomal hydroxylase-characterization and reconstitution of its activity

Arınç, Emel
Aydoǧmuş, Aydan
1. Formation of catechols from benzene and nitrobenzene have been implicated in the carcinogenic activity of these chemicals. In liver, , an intermediate of is enzymatically converted to 4-nitrocatechol. 2. 2. For the first time in this study, the presence of a highly active enzyme catalyzing the formation of 4-nitrocatechol from was detected in lung microsomes. The average specific activity of lung hydroxylase was found to be 0.494 nmol 4-nitrocatechol formed mg prot−1 min−1. 3. 3. The optimum conditions for sheep lung microsomal hydroxylase were established. The maximal activity was noted at pH 6.8. The rate of hydroxylation was linear up to 2 mg prot/ml of incubation mixture. The maximal rate of 4-nitrocatechol formation was observed with 0.25 mM . 4. 4. The Lineweaver-Burk and Eadie-Hofstee plots were found to be curve-linear. Two different values were calculated as 11.6 and 71.4 μM from the Lineweaver-Burk plot and as 10.7 and 74.5 μM from the Eadie-Hofstee plot. This suggested that there were either two forms of enzyme or two different enzymes participating in ortho hydroxylation of in lung microsomes. 5. 5. Lung microsomal hydroxylase activity of sheep was reconstituted in the presence of purified lung microsomal cytochrome P-450, NADPH dependent cytochrome P-450 reductase and synthetic lipid, phosphatidylcholine dilauroyl.