NAD-malic enzyme (EC 1.1.1.39) was purified from bundle sheath strands of Urochloa panicoides (a phosphoenolpyruvate carboxykinase-type C4 plant) and its kinetic and regulatory properties were investigated. The native enzyme has a molecular weight of about 470 000 and is an octomer composed of two slightly different monomers which occur in a 1 : 1 ratio. The enzyme has an absolute requirement for Mn2+, is stimulated by CoA, acetyl CoA, fructose 1,6-bisphosphate and SO42- and is inhibited by HCO3, oxaloacetate, 2-oxoglutarate and pyruvate. The enzyme is shown to be localised in the mito- chondria. The purified NAD-malic enzyme is unable to catalyse the carboxylation of pyruvate according to the reverse reaction. These findings are discussed in relation to the C4 photosynthetic pathway and its possible role in PEP carboxykinase-type C4 plants.
Phosphate Translocator of Mesophyll and Bundle Sheath Chloroplasts of a C4 Plant, Panicum miliaceum L.