Characteristics and physiological function of NADP-malic enzyme from wheat

Kinetic and structural properties of NADP-malic enzyme (NADP-ME, EC 1.1.1.40) purified from stems and roots of wheat (Triticum aestivum), along with the possible physiological role of the enzyme were examined, Enzyme purification from stems sequentially involved precipitation with crystalline ammonium sulfate, anion-exchange, affinity and size exclusion chromatographies, while anion-exchange chromatography was omitted for the enzyme purification from roots, SDS-PAGE of the purified enzyme showed a single protein band with a molecular mass of 72-kDa, Enzyme activity was dependent on the presence of a bivalent metal cation, Mg2+ or Mn2+, Binding characteristics of each metal ion suggest the existence of at least two different binding sites with distinct affinities, Nonetheless, activity response to NADP(+) and L-malate exhibited Michaelis-Menten behavior with K-m values of 37 and 960 mu M, respectively. The amount and activity of NADP-ME were increased by GSH, cellulase and macerozyme. From these results we suggest that NADP-ME of wheat could be implicated in defense-related deposition of lignin.