TY  - JA
AU  - Pascal,S.
AU  - Rahier,A.
AU  - Taton,M.
TI  - Plant sterol biosynthesis:  identification of a NADPH dependent sterone reductase involved in sterol-4 demethylation
SN  - 0003-9861
U1  - 95-099007 
PY  - 1994///
KW  - Biochemical reactions
KW  - Carbohydrates
KW  - Cell structure
KW  - Chemical reactions
KW  - Cofactors
KW  - Cytoplasm
KW  - Developmental stages
KW  - Enzymes
KW  - Glycosides
KW  - Gramineae
KW  - Nucleic compounds
KW  - Plant developmental stages
KW  - Plant physiology and biochemistry
KW  - Protoplasm
KW  - Steroids
KW  - Sterols
KW  - Zea
N1  - references US (DNAL 381 Ar2)
N2  - Microsomes obtained from maize embryos were shown to catalyze the reduction of various sterones to produce stereoselectively the corresponding 3,6-hydroxy derivatives. Enzymatic assay conditions have been developed to characterize this reduction step and the kinetics of the microsomal system has been established. Sterone reduction shows exclusive dependence on NADPH and is inactive with NADH. It is not sensitive to the azole inhibitors pyrifenox, ketoconazole, and itraconazole nor to phenobarbital nor pyrazole. Based on these coenzyme requirements and inhibitor susceptibility, and according to the common pattern of their classification, the maize microsomal sterone-reducing enzyme belongs to the family of ketone reductases. From a series of incubations with natural or synthetic sterones, the substrate specificity of the reduction at C-3 was determined. Our data indicate particularly that 4 alpha-methyl-9,6,19-cyclo-C30-sterones and 4-desmethyl-delta 7-C27- or C30-sterones are preferentially reduced, while 4,4-dimethyl-C30- or C31-sterones react poorly. The results support the conclusion that the reductase activity identified is a constitutive component of the microsomal sterol 4-demethylation complex recently identified in photosynthetic organisms (S. Pascal et al., 1993, J. Biol. Chem. 268, 11639). They are consistent with the conclusion that 4 alpha-methylsterones are demethylation products of 4,4-gem-dimethylsterols rather than early intermediates in the 4 alpha-monomethylsterols-4-demethylation process
T2  - Archives of biochemistry and biophysics (USA). (Jul 1994). v. 312(1) p. 260-271
ER  -