Existence and Properties of Two Malic Enzymes in Escherichia coliEspecially of NAD-linked Enzyme

Abstract

It was demonstrated that an NAD-linked malic enzyme [EC 1. 1. 1. 38] is present in E. coli in addition to the NADP-linked malic enzyme [EC 1.1. 1.40]. The NAD-linked malic enzyme was purified about 100-fold and some of its properties were examined. This enzyme was different from many other malic enzymes in that it required no monovalent cation for its activity and did not undergo substrate inhibition. The apparent Km values for malate and for NAD were 9x10-4 and 4.7X1O5M, respectively, at pH7.9. The value for Mn2 at 10mM of malate was l.5xl05M, at the same pH value. It was observed that the higher the Concentration of malate, the higher was the affinity for Mn2. The optimum pH for the enzyme activity varied depending upon the concentration of malate and showed 7.5 at 0.01 M malate. This enzyme showed an oxaloacetate decarboxylating activity. The optimum pH for this activity was 4.5. It was inhibited by NAD. The partially purified NADP-linked malic enzyme from E. coli was similar to those from other sources in many respects, except that it showed a full activity in the presence of adequate amounts of NH4.