NADP malic enzyme (EC 18.104.22.168) from leaves of two C4 species of Cyperus (C. rotundus and C. brevifolius var leiolepis) exihibited a low level of activity in an assay mixture that contained low concentrations of Cl-. This low level of activity was markedly enhanced by increases in the concentration of NaCl up to 200 mM. Since the activity of NADP malic enzyme was inhibited by Na2SO4 and stimulated by relatively high concentration of Tris-HCl (50-100 mM, pH 7-8), the activation of the enzyme by NaCl appears to be due to Cl-. Variations in the concentration of Mg2+ affected the KA (the concentration of activator giving half-maximal activation) for Cl-, which decreased from 500 mM to 80 mM with increasing concentrations of Mg2+ from 0.5 mM to 7 mM. The Km for Mg2+ was decreased from 7.7 mM to 1.3 mM with increases in the concentration of NaCl from zero to 200 mM, although the increase of Vmax was not remarkable. NADP malic enzyme from Cyperus, being similar to that from other C4 species, was able to utilize Mn2+. The Km for Mn2+ was 5 mM, a value similar to that for Mg2+. The addition of 91 mM NaCl markedly decreased the Km for Mn2+ to 20 +M. NADP malic enzyme from Setaria glauca, which contains rather less Cl- than other C4 species, was inactivated by concentrations of NaCl above 20 mM, although slight activation of the enzyme was observed at low concentrations of NaCl at pH7.6.
|Number of pages||5|
|Journal||Plant and Cell Physiology|
|Publication status||Published - Jan 1 1989|
All Science Journal Classification (ASJC) codes
- Plant Science
- Cell Biology