7-Oxo-24,25-dihydrolanosterol: a novel lanosterol 14 alpha-demethylase (P-45014DM) inhibitor which blocks electron transfer to the oxyferro intermediate.
7-Oxo-24,25-dihydrolanosterol (3 beta-hydroxy-8-lanosten-7-one, 7-oxo-HDL) was a potent competitive inhibitor for lanosterol 14 alpha-demethylase (cytochrome P-45014DM) of Saccharomyces cerevisiae. Affinity of 7-oxo-DHL for the enzyme was more than 50-times higher than those of the inherent substrates, lanosterol and 24,25-dihydrolanosterol. 7-Oxo-DHL accelerated NADPH-dependent reduction of cytochrome P-45014DM in the reconstituted system consisting of the cytochrome and NADPH-cytochrome P-450 reductase. These observations indicated that 7-oxo-DHL interacted with the substrate site of cytochrome P-45014DM. However, 7-oxo-DHL was not metabolized by the reconstituted system. Incubation of 7-oxo-DHL with the reconstituted system caused accumulation of oxyferro intermediate of cytochrome P-45014DM. It can thus be concluded that 7-oxo-DHL interfered with electron transfer to the oxyferro intermediate of the cytochrome, though it stimulated reduction of the heme iron. So far as we know, 7-oxo-DHL is the first example of a cytochrome P-450 inhibitor which selectively interferes with the electron transfer to oxyferro intermediate. 7 alpha-Hydroxy-24,25-dihydrolanosterol was also a competitive inhibitor of cytochrome P-45014DM. However, this compound was metabolized by the reconstituted system and could not block the electron transfer to oxyferro intermediate. 11-Oxo-24,25-dihydrolanosterol, an isomer of 7-oxo-DHL, did not have such inhibitory effects. These lines of evidence suggest a possibility that the keto group at C-7 of lanost-8-ene skeleton may interact with a certain site of cytochrome P-45014DM which has an important role in the electron transfer to oxyferro intermediate.
Aoyama
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Y
Faculty of Pharmaceutical Sciences, Mukogawa Women's University, Hyogo, Japan.
Yoshida
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Sonoda
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Sato
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Y
D002849:Chromatography, Gas; D003577:Cytochrome P-450 Enzyme System; D004579:Electron Transport; D007700:Kinetics; D007810:Lanosterol / Q000031:analogs & derivatives* / Q000494:pharmacology; D013058:Mass Spectrometry; D010088:Oxidoreductases / Q000037:antagonists & inhibitors*; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D058886:Sterol 14-Demethylase
D007810:Lanosterol; C047418:7-oxo-24,25-dihydrolanosterol; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D058886:Sterol 14-Demethylase