COMPARATIVE EFFECTS OF ANTHELMINTICS ON C-MDH FROM MOLINEMA-DESSETAE (NEMATODA, FILARIOIDEA) AND FROM A MAMMAL

Malate dehydrogenase (MDH) (E.C.1.1.1.37) activity was detected in the filaria Molinema dessetae at a level similar to those found in other filariae. In M. dessetae, the cytoplasmic form (c-MDH) predominated an d the study was performed on partially purified fractions. The pH opti mum for oxaloacetate reduction was 6.1, with maximal activity at 7811 nmol min-1 mg protein-1, but high concentrations of oxaloacetate inhib ited MDH activity. The K(m) value for oxaloacetate was determined as 2 2 muM for M. dessetae c-MDH and 33 muM for mammalian c-MDH. Anthelmint ic drugs were compared as potential inhibitors of filarial and mammali an c-MDH. Among the compounds evaluated, amocarzine showed a specific inhibitory effect on filarial c-MDH through only at high concentration s. Suramin alone showed an inhibitory effect at low concentrations (K( i) = 1.15 muM) but without selective action towards filarial c-MDH. Th e suramin type of inhibition was found to be competitive. Suramin prob ably acts on both enzymes in the same manner. Nevertheless, M. desseta e c-MDH is proposed as a suitable enzyme assay model to screen MDH inh ibitors as potential filaricides.