title: Isolation and characterization of an altered cytochrome P-450 from a yeast mutant defective in lanosterol 14 alpha-demethylation.
abstract: A cytochrome P-450 (P-450SG1) was purified from a lanosterol 14 alpha-demethylase (P-450(14DM)) defective mutant of Saccharomyces cerevisiae, strain SG1, by a method similar to that used in the purification of the wild type enzyme (Yoshida, Y., and Aoyama, Y. (1984) J. Biol. Chem. 259, 1655-1660). P-450SG1 had the same apparent Mr as and was immunochemically identical to P-450(14DM). Peptide maps of P-450SG1 made by limited proteolysis with Staphylococcus aureus V8 proteinase, chymotrypsin, or papain followed by gel electrophoresis were identical to corresponding peptide maps of P-450(14DM). However, P-450SG1 showed no lanosterol 14 alpha-demethylase activity and its mode of interaction with diniconazole [(E)-1-(2,4-dichlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-y1)-1- penten-3- o1], a specific inhibitor of P-450(14DM), was fundamentally different from that of P-450(14DM). The absorption spectrum of ferric P-450SG1 was unusual for a native low-spin cytochrome P-450 and was superimposable on that of 1-methylimidazole complex of P-450(14DM), indicating that P-450SG1 has a histidine 6th ligand trans to the thiolate 5th ligand, while the 6th ligand of other ferric low-spin cytochrome P-450s is a water molecule or a hydroxyl group of an oxyamino acid. It is concluded that P-450SG1 is an altered P-450(14DM). Difference in the primary structure between P-450SG1 and P-450(14DM) may be slight and was not detected by peptide mapping. However, the alteration caused significant change in the substrate site and heme environments of the cytochrome. P-450SG1 is the first example of a cytochrome P-450 having a histidine axial ligand trans to thiolate and of a genetically altered cytochrome P-450 isolated in a homogeneous state.
mesh_terms: D003577:Cytochrome P-450 Enzyme System / Q000302:isolation & purification* / Q000378:metabolism; D006418:Heme / Q000378:metabolism; D005779:Immunodiffusion; D007810:Lanosterol / Q000378:metabolism*; D008861:Microsomes / Q000201:enzymology; D009154:Mutation; D010088:Oxidoreductases / Q000235:genetics*; D010449:Peptide Mapping; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D013053:Spectrophotometry; D058886:Sterol 14-Demethylase
chemical_list: D007810:Lanosterol; D006418:Heme; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D058886:Sterol 14-Demethylase