The Enzyme Kinetics of the NADP-Malic Enzyme from Tobacco Leaves
| Autor: | Petra Baťková, Renáta Schnablová, Veronika Doubnerová, Helena Synková, Karel Müller, Noemi Čeřovská, Jiří Liberda, Helena Ryšlavá |
|---|---|
| Rok vydání: | 2007 |
| Předmět: | |
| Zdroj: | Collection of Czechoslovak Chemical Communications. 72:1420-1434 |
| ISSN: | 1212-6950 0010-0765 |
| DOI: | 10.1135/cccc20071420 |
| Popis: | Malic enzyme (L-malate: NADP+ oxidoreductase (oxaloacetate-decarboxylating), EC 1.1.1.40, NADP-ME), which was found in chloroplasts, was isolated from tobacco leaves (Nicotiana tabacum L.) almost homogenous. The specific enzyme activity was 0.95 μmol min-1 mg-1. The enzyme pH optimum was found between pH 7.1 and 7.4. The affinity of NADP-ME to substrates (L-malate and NADP+) was evaluated in the presence of divalent metal ions (Mg2+, Mn2+, Co2+, Ni2+). The value of the apparent Michaelis constant of NADP-ME for L-malate was dependent on the ion cofactor, while no such relationship was found for NADP+. The dependence of the reaction rate on concentration of Mg2+ indicates the presence of more than one binding site for these ions in NADP-ME. Likewise, the sigmoidal dependence of the reaction rate on Mn2+ concentration and the value of Hill coefficient 7.5 indicate the positive cooperativity of the reaction kinetics in the presence of the ions. The effect of Co2+ and Ni2+ ions was analogous to that of Mn2+ ions; however, the cooperativity was lower (the values of Hill coefficients were 3.0 and 1.3 for Co2+ and Ni2+, respectively). Regulation of NADP-ME from tobacco leaves by divalent metal ions is discussed. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|