Comparative Studies of NAD-Malic Enzyme from Leaves of Various C_4 Plants

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Using butyl-TSK-gel chromatography, we purified NAD-malic enzyme (ME) (EC 1.1.1.39), which is involved in C_4 photosynthesis, to electrophoretic homogeneity, from leaves of Amaranths tricolor. Molecular weights of the native and SDS-denatured enzyme from A. tricolor were 490 kDa and 61 kDa, respectively. During assay of the enzyme there was a slow reaction transient in the form of a lag before a steady-state rate was reached. The duration of this lag was inversely proportional to the concentration of each substrate and the activator, fructose-1,6-bisphosphate (FBP). The optimal pH of the reaction fell with decreasing concentrations of either malate or FBP. High pH prolonged the lag in reaction. Double reciprocal plots of the enzymatic activity as a function of the concentration of malate yielded straight lines and did not show any cooperativity for binding of malate. The enzyme from A. tricolor was not inhibited by either HCO_3^- or CO_2・ At different concentrations of malate, the nature of the activating effect of FBP was compared among the purified enzymes from A. tricolor and the C_4 monocots Eleusine coracana and Panicum dichotonaflorum. At low levels of malate, FBP markedly stimulated the enzyme from each species. In contrast, at saturating levels of malate, the response of enzymes to increasing concentrations of FBP was different and depended on the source of enzyme. The immunochemical properties of the enzymes from the three species were compared using an enzyme-linked immunoadsorbent assay with antisera raised against the purified enzymes from the three species. Different cross-reactivities were observed among the enzymes from different sources. The N-terminal amino acid sequences of NAD-MEs from the three species were deter-mined and some differences were found among the three enzymes.
日本植物生理学会の論文

Comparative Studies of NAD-Malic Enzyme from Leaves of Various C_4 Plants

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