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  • Title: The role of cytochrome b5 in 4alpha-methyl-oxidation and C5(6) desaturation of plant sterol precursors.
    Author: Rahier A, Smith M, Taton M.
    Journal: Biochem Biophys Res Commun; 1997 Jul 18; 236(2):434-7. PubMed ID: 9240456.
    Abstract:
    The electron donors for the membrane-bound sterol-4alpha-methyl-oxidases and sterol C5(6)-desaturase of plant sterol biosynthesis have not been previously identified. The requirement of cytochrome b5 to shuttle reducing equivalents from NAD(P)H to 4,4-dimethylsterol-4alpha-methyl oxidase (4,4-DMSO), 4alpha-methylsterol-4alpha-methyl oxidase (4alpha-MSO), and delta7-sterol-C5(6) desaturase (5-DES) was investigated using a purified preparation of IgG raised against plant cytochrome b5. The activities of 4,4-DMSO, 4alpha-MSO, and 5-DES, three oxidative reactions not mediated by cytochrome P-450, were strongly and completely inhibited by the antibody in a microsomal preparation from maize. In addition the IgG also inhibited NADH-dependent cytochrome c reduction in the same preparation. These results strongly suggest that membrane-bound cytochrome b5 of maize microsomes is an obligatory electron carrier from NAD(P)H to 4,4-DMSO, 4alpha-MSO, and 5-DES.
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