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) sho wed potent noncompetitive inhibition of bacterial squalene:hopene cycl ase (SHC) from Alicyclobacillus acidocaldarius (IC50 = 9.0 nM, K-I = 6 .6 nM) and OSLC (IC50 = 40 nM, K-I = 22 nM for homogeneous rat liver O SLC). A tritium-labeled isotopomer (18.8 Ci/mmol) of this nonterpenoid inhibitor, which possesses a benzophenone (BP) photophore, was chemic ally synthesized as a photoaffinity label. Specific, efficient covalen t modification of both OSLC and SHC enzymes was observed after UV irra diation at 360 nm. Labelling of both OSLC and SHC by [H-3]Ro48-8071 wa s competitively displaced by coincubation with a 1000-fold molar exces s of 18-thia-2,3-oxidosqualene or the nonterpenoid inhibitor BIBX79. D isplacement of labelling of OSLC was also achieved with the suicide su bstrate (3S)-29-methylidene-2,3-oxidosqualene. Thus, the nonsubstrate Ro48-8071 and both terpenoid and nonterpenoid inhibitors of these enzy mes appear to share a common binding site.