| Abstract: | Kinetic properties of purified chloroplast isoenzyme of the "malic" enzyme from corn leaves were studied. The enzyme had optimum activity at pH 8.0 and 36 degrees C. Under standart conditions the Michaelis constants for the "malic" enzyme with Mn2+ as cofactor are 0.091 mM for malate and 0.04 mM for NADP. In case of Mg2+ as cofactor they are 0.66 and 0.02 mM respectively. Respective Km values for the cofactors Mn2+ and Mg2+ are 0.018 and 0.091 mM. The activity of the "malic" enzyme was inhibited by reduced NADP and NAD, ATP, ADP, fructose-1,6-diphosphate, oxaloacetic, oxalic, glyoxylic, glycolic and alpha-ketoglutaric acids, as well as by phosphate anions and pyrophosphate. The inhibitory effect of all metabolites and ions is more pronounced in case of Mn, rather than Mg, used as cofactors for the reaction. A possibility of metabolic regulation of NADP-"malic" enzyme activity in the leaves of C4-plants, is discussed. |
