title: Biosynthesis of rice phytoalexin: enzymatic conversion of 3beta-hydroxy-9beta-pimara-7,15-dien-19,6beta-olide to momilactone A.
abstract: Momilactone A, a major rice diterpene phytoalexin, could be synthesized by dehydrogenation at the 3-position of 3beta-hydroxy-9beta-pimara-7,15-dien-19,6beta-olide in rice leaves. The presence of 3beta-hydroxy-9beta-pimara-7,15-dien-19,6beta-olide in UV-irradiated rice leaves was confirmed by comparing the mass spectra and retention times after a GC/MS analysis of the natural and synthetic compounds. The soluble protein fraction from UV-irradiated rice leaves showed dehydrogenase activity to convert 3beta-hydroxy-9beta-pimara-7,15-dien-19,6beta-olide into momilactone A. The enzyme required NAD+ or NADP+ as a hydrogen acceptor. The optimum pH for the reaction was 8. The Km value to 3beta-hydroxy-9beta-pimara-7,15-dien-19,6beta-olide was 36 microM when NAD+ was supplied as a cofactor at a concentration of 1 mM. 3fl-Hydroxy-9beta-pimara-7,15-dien-19,6beta-olide and its dehydrogenase activity were induced in a time-dependent manner by UV irradiation.
authors: United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology, Fuchu-shi, Japan.
authors: Anotai
authors: A
authors: Atawong
authors: Morifumi
authors: M
authors: Hasegawa
authors: Osamu
authors: O
authors: Kodama
mesh_terms: D004224:Diterpenes / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D006863:Hydrogen-Ion Concentration; D012275:Oryza / Q000201:enzymology / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism; D010936:Plant Extracts / Q000096:biosynthesis*; D018515:Plant Leaves / Q000737:chemistry; D010940:Plant Proteins / Q000378:metabolism; D012717:Sesquiterpenes; D013056:Spectrophotometry, Ultraviolet; D013347:Subcellular Fractions / Q000201:enzymology; D013729:Terpenes; D014466:Ultraviolet Rays; D000094162:Phytoalexins
chemical_list: D004224:Diterpenes; D010936:Plant Extracts; D010940:Plant Proteins; D012717:Sesquiterpenes; D013729:Terpenes; C099622:pimara-7,15-diene; C116023:momilactone A; D010088:Oxidoreductases; D000094162:Phytoalexins