Antagonism between cadmium chloride and divalent metal cations in the activation of malic enzyme

Abstract

1. The effect of the divalent cation on the activation of the shrimp Crangon crangon abdomen muscle cytosol NADP-dependent malic enzyme (EC 1.1.1.40) and herring Clupea harengus testicular tissue mitochondrial NAD(P)-dependent malic enzyme (EC 1.1.1.39) was examined. 2. For cytosol the NADP-dependent malic enzyme K m for manganese is only slightly higher than that for cadmium and cobalt, while it is about 60-times lower than the value for magnesium. 3. For the mitochondrial NAD(P)-dependent malic enzyme in the NAD linked reaction K m for manganese is very similar to that for cobalt, while it is 2.7-fold and 41-fold lower than the value for cadmium and magnesium, respectively. In the NADP linked reaction, K m for manganese is only slightly higher than that for cobalt, while it is 1.6-fold and 36-fold lower than the value for cadmium and magnesium, respectively. 4. The cadmium ion shows strong inhibition of the malic enzyme activity. In cation combinations, cadmium causes inhibition of enzyme activity to the value as added alone only. These results demonstrate that malic enzyme is a molecule which is very sensitive to cadmium exposure.