Photoaffinity labeling of oxidosqualene cyclase and squalene cyclase by a benzophenone-containing inhibitor.
A new orally active oxidosqualene:lanosterol cyclase (OSLC) inhibitor (Ro48-8071; Morand, O. H. et al. (1997) J. Lipid Res. 38, 373-390) showed potent noncompetitive inhibition of bacterial squalene:hopene cyclase (SHC) from Alicyclobacillus acidocaldarius (IC50 = 9.0 nM, KI = 6.6 nM) and OSLC (IC50 = 40 nM, KI = 22 nM for homogeneous rat liver OSLC). A tritium-labeled isotopomer (18.8 Ci/mmol) of this nonterpenoid inhibitor, which possesses a benzophenone (BP) photophore, was chemically synthesized as a photoaffinity label. Specific, efficient covalent modification of both OSLC and SHC enzymes was observed after UV irradiation at 360 nm. Labeling of both OSLC and SHC by [3H]Ro48-8071 was competitively displaced by coincubation with a 1000-fold molar excess of 18-thia-2, 3-oxidosqualene or the nonterpenoid inhibitor BIBX79. Displacement of labeling of OSLC was also achieved with the suicide substrate (3S)-29-methylidene-2,3-oxidosqualene. Thus, the nonsubstrate Ro48-8071 and both terpenoid and nonterpenoid inhibitors of these enzymes appear to share a common binding site.
Abe
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I
Department of Medicinal Chemistry, The University of Utah, Salt Lake City 84112-5820, USA.
Zheng
Y F
YF
Prestwich
G D
GD
D000818:Animals; D001406:Bacillaceae / Q000201:enzymology; D001577:Benzophenones / Q000378:metabolism* / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000378:metabolism* / Q000494:pharmacology; D019751:Intramolecular Transferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007700:Kinetics; D008190:Lyases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology; D019920:Photoaffinity Labels / Q000378:metabolism*; D011487:Protein Conformation; D051381:Rats; D013379:Substrate Specificity / Q000187:drug effects
D001577:Benzophenones; D004791:Enzyme Inhibitors; D019920:Photoaffinity Labels; C105726:Ro 48-8071; D008190:Lyases; C022651:squalene cyclase; D019751:Intramolecular Transferases; C021924:lanosterol synthase