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A method is described for the purification of the enzyme phosphoenolpyruvate carboxykinase (PEPCK) from the cestode Hymenolepis diminuta. When purified to electrophoretic homogeneity, the enzyme had a molecular weight of 70,600 and an isoelectric point of 7.5. Kinetic studies indicated that the pH 5.6 was optimal for the carboxylation reaction and that Mn++ was the preferred divalent cation; there was no activity of the enzyme in the presence of Mg++. Apparent Km values for the carboxylation reaction were determined; those for GDP (20.6 muM) and PEP (38.9 muM) were lower than the values previously reported. GTP, GMP, ITP, IMP, fumarate, succinate and alpha-ketoglutarate were found to be competitive inhibitors and their Ki values determined.

Formulated mebendazole was administered to sheep by intraruminal injection at dose rates of 12.5, 25, 50 or 100 mg/kg bodyweight. The concentrations of mebendazole and two major metabolites were measured by high-performance liquid chromatography in plasma taken at intervals up to 48 hours after treatment. At 12.5 mg/kg the peak plasma concentration was 0.22 +/- 0.03 microM mebendazole, rising to 0.76 +/- 0.04 microM at 100 mg/kg. Peak plasma concentrations occurred between nine and 24 hours for all dose rates and declined rapidly. Two major metabolites were detected; their concentrations exceeded that of mebendazole at all dose rates.

Procedures have been developed for the extraction and subsequent purification of the enzyme phosphoenolpyruvate carboxykinase (GTP) (PEPCK) from Moniliformis dubius (Acanthocephala), a parasite of the rat small intestine. This is believed to be the first purification of PEPCK from an invertebrate animal. The enzyme, when purified to homogeneity as indicated by electrophoretic criteria, has a molecular weight of 73 700. Kinetic studies indicated that the enzyme had a pH optimum of 5.5 and required Mn2+ as the divalent cation. The apparent Km values determined for the substrates of the carboxylation reaction were low compared with the published values for purified PEPCK from vertebrate sources. Several competitive inhibitors were found and their Ki values determined. The possible regulation of PEPCK activity in M. dubius is discussed with reference to the observed kinetic parameters.