Biosynthesis of rice phytoalexin: enzymatic conversion of 3beta-hydroxy-9beta-pimara-7,15-dien-19,6beta-olide to momilactone A

Biosci Biotechnol Biochem. 2002 Mar;66(3):566-70. doi: 10.1271/bbb.66.566.

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.

MeSH terms

  • Diterpenes / metabolism*
  • Gas Chromatography-Mass Spectrometry
  • Hydrogen-Ion Concentration
  • Oryza / enzymology
  • Oryza / metabolism*
  • Oxidoreductases / metabolism
  • Plant Extracts / biosynthesis*
  • Plant Leaves / chemistry
  • Plant Proteins / metabolism
  • Sesquiterpenes
  • Spectrophotometry, Ultraviolet
  • Subcellular Fractions / enzymology
  • Terpenes
  • Ultraviolet Rays

Substances

  • Diterpenes
  • Plant Extracts
  • Plant Proteins
  • Sesquiterpenes
  • Terpenes
  • pimara-7,15-diene
  • phytoalexins
  • momilactone A
  • Oxidoreductases