Purification and characterization of two unique forms of cytochrome P-450 from rabbit nasal microsomes.
Two forms of cytochrome P-450, designated P-450NMa and P-450NMb, were purified to electrophoretic homogeneity from rabbit nasal microsomes. The purified cytochromes, which contained 14-16 nmol of P-450/mg of protein, exhibited apparent monomeric molecular weights of 49,500 and 51,000, respectively. As indicated by several criteria, including the amino acid composition, absorption spectra, and peptide maps, the two nasal forms of P-450 are distinct from each other. Furthermore, as judged by the NH2-terminal amino acid sequences, they are distinct from all other P-450 cytochromes described to date. In the ferric form, P-450NMa is in the low-spin state, whereas P-450NMb is predominantly in the high-spin state. When reconstituted with NADPH-cytochrome P-450 reductase and phospholipid, P-450NMa is very active in the oxidation of ethanol as well as several nasal procarcinogens, including the N-deethylation of N-nitrosodiethylamine, the O-deethylation of phenacetin, and the N-demethylation of hexamethyl-phosphoramide. P-450NMb also metabolizes these substrates, but at lower rates. Both nasal forms are also active with testosterone, with P-450NMa oxidizing the substrate in the 17-position to give androstenedione and P-450NMb catalyzing hydroxylation in the 15 alpha-, 16 alpha-, and 19-positions. The two cytochromes represent the major portion of the total P-450 in nasal microsomes, but the corresponding forms could not be detected in hepatic microsomes.
Ding
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Department of Biological Chemistry, Medical School, University of Michigan, Ann Arbor 48109.
Coon
M J
MJ
D000595:Amino Acid Sequence; D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000302:isolation & purification* / Q000378:metabolism; D007527:Isoenzymes / Q000302:isolation & purification* / Q000378:metabolism; D008297:Male; D008861:Microsomes / Q000201:enzymology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009666:Nose / Q000201:enzymology*; D010446:Peptide Fragments / Q000302:isolation & purification; D011817:Rabbits; D013057:Spectrum Analysis; D013379:Substrate Specificity
D007527:Isoenzymes; D010446:Peptide Fragments; D003577:Cytochrome P-450 Enzyme System