Localization of the N-terminal methionine of rat liver cytochrome P-450 in the lumen of the endoplasmic reticulum |
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Authors: | G Vergères K H Winterhalter C Richter |
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Affiliation: | Laboratorium für Biochemie, Eidgen?ssische Technische Hochschule, ETH-Zentrum, Zürich, Switzerland. |
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Abstract: | Recent cumulative evidence suggests that liver microsomal cytochrome P-450 (P-450) is exposed to the cytosol with the exception of the N-terminal peptide (amino acid residues 1 to 21), or two peptides (residues 1 to 60). We tested the localization of the N-terminal methionine residue of P-450IIB1 of rat liver microsomes in the natural membrane with the site-specific reagent fluorescein isothiocyanate. The N-terminus of isolated P-450 was stoichiometrically modified in solution with fluorescein isothiocyanate. In intact microsomes, the N-terminus was not modified but became accessible to the reagent when the membrane was dissolved with Triton X-100. Our results indicate that the N-terminus faces the lumen of the endoplasmic reticulum, and we propose that P-450 spans the membrane only once with amino acid residues 1 to 21. |
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