The role of cytochrome b5 in 4alpha-methyl-oxidation and C5(6) desaturation of plant sterol precursors.
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.
Rahier
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A
Département d'Enzymologie Cellulaire et Moléculaire, Institut de Biologie Moléculaire des Plantes, CNRS UPR 406, Strasbourg, France. enzymo@bota-ulp.u-strasbg.fr
Smith
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M
Taton
M
M
D015786:Cytochromes b5 / Q000378:metabolism*; D008745:Methylation; D008861:Microsomes / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009245:NADH Dehydrogenase / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D013261:Sterols / Q000378:metabolism*; D003313:Zea mays / Q000201:enzymology / Q000378:metabolism*
D013261:Sterols; D015786:Cytochromes b5; D006899:Mixed Function Oxygenases; D010088:Oxidoreductases; C027532:methylsterol monooxygenase; C039306:sterol delta-5 desaturase; D009245:NADH Dehydrogenase