Partial purification and comparison of the kinetic properties of ovine liver Echinococcus granulosus hydatid cyst fluid malate dehydrogenase and the cytoplasmic enzyme from the host liver.

Ovine liver Echinococcus granulosus hydatid cyst fluid and cytoplasmic healthy ovine liver malate dehydrogenases were purified 24- and 30-fold by Sephadex G-200 and DEAE-Sephadex chromatography. Both enzymes were eluted with the same elution volume and the same salt concentration from the respective columns. The pH optimum of the enzymes from both sources was 8.4 in either Tris-HCl or barbital buffer. The Km values for oxaloacetate were 0.211 and 0.200 mM for hydatid cyst fluid and healthy ovine liver enzymes, respectively. The Km values for NADH were 0.220 and 0.213 mM for hydatid cyst fluid and healthy ovine liver enzymes, respectively. Enzyme from both sources demonstrated similar heat denaturation patterns. Both enzyme preparations were inhibited at high concentrations of either substrate. Neither enzyme was inhibited by para-hydroxymercuribenzoate or fumarate, and both enzyme preparations were specific for NADH as a cofactor. The results are discussed in terms of the possible infiltration of the host enzyme into the cyst fluid.