Enzymes of octadecanoid biosynthesis in plants--12-oxo-phytodienoate 10,11-reductase.

Octadecanoids, potent cyclic plant signaling molecules derived from alpha-linolenic acid, are involved in the regulation of a multitude of physiological processes such as senescence, herbivore and pathogen defense, mechanoperception and morphogenesis. The first cyclic intermediate in the Vick-Zimmerman pathway of octadecanoid biosynthesis is 12-oxo-phytodienoic acid. Its conversion to the end product of the pathway, jasmonic acid, a C12 compound, first proceeds through reduction to 3-oxo-2-(pent-2'-enyl)-cyclopentane-1-octanoic acid, which is then converted to jasmonic acid by three cycles of beta-oxidation. The first of these conversions is a decisive point in the biosynthetic sequence, in that it channels the octadecanoid into the pathway of beta-oxidation. 12-Oxo-phytodienoate reductase was purified to apparent homogeneity from a cell suspension culture of Corydalis sempervirens. The enzyme is soluble and a monomer of apparent molecular mass 41 kDa which prefers NADPH over NADH to reduce the 10,11-double bond of 12-oxo-phytodienoic acid. The structure of the reaction product was proved by derivatization, GC/MS and NMR analysis. The enzyme accepts both the cis and the trans isomer of 12-oxo-phydodienoic acid, with a preference for the cis-isomer (6:1). 12-Oxo-phytodienoate reductase will also convert the synthetic substrate 2-cyclohexenone to cyclohexanone, but the enzyme did not reduce some other cyclic alpha,beta-unsaturated ketones tested (the plant hormone abscisic acid or the steroids testosterone and progesterone). Characteristic parameters of 12-oxo-phytodienoate reductase were determined.