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 EC] ) purified from stems and roots of wheat (Triticumaestivum), along with the possible physiological role of theenzyme were examined. Enzyme purification from stems sequentiallyinvolved precipitation with crystalline ammonium sulfate, anion-exchange,affinity and size exclusion chromatographies, while anion-exchangechromatography was omitted for the enzyme purification fromroots. SDS-PAGE of the purified enzyme showed a single proteinband with a molecular mass of 72-kDa. Enzyme activity was dependenton the presence of a bivalent metal cation, Mg²⁺ or Mn²⁺. Bindingcharacteristics of each metal ion suggest the existence of atleast two different binding sites with distinct affinities.Nonetheless, activity response to NADP⁺ and L-malate exhibitedMichaelis-Menten behavior with K_m values of 37 and 960 µM,respectively. The amount and activity of NADP-ME were increasedby GSH, cellulase and macerozyme. From these results we suggestthat NADP-ME of wheat could be implicated in defense-relateddeposition of lignin. ¹Both authors contributed equally to this work.