PURIFICATION AND CHARACTERIZATION OF ISOCITRATE LYASE FROM ETHANOL-GROWN EUGLENA-GRACILIS

Isocitrate lyase was purified to homogeneity from ethanol-grown Euglen a gracilis. The specific activity was 0.26 mu mol/min/mg protein. The molecular mass of the enzyme was calculated to be 380 kDa by gel filtr ation on a Superose 6 column. The subunit molecular mass of the enzyme was 116 kDa as determined by SDS-polyacrylamide gel electrophoresis. These results showed that the native form of this enzyme was a trimer composed of three identical subunits. The pH optimum for cleavage and condensation reactions was 6.5 and 7.0, respectively. The K-m values f or isocitrate, glyoxylate and succinate were 3.8, 1.3 and 7.7 mM, resp ectively. Isocitrate lyase absolutely required Mg+ for enzymatic activ ity. This is the first report of the purification of isocitrate lyase to homogeneity from Euglena gracilis.