PYRUVATE-DEHYDROGENASE COMPLEXES FROM THE EQUINE NEMATODE, PARASCARIS-EQUORUM, AND THE CANINE CESTODE, DIPYLIDIUM-CANINUM, HELMINTHS EXHIBITING ANAEROBIC MITOCHONDRIAL METABOLISM

The pyruvate dehydrogenase complex (PDC) has been purified to apparent homogeneity from 2 parasitic helminths exhibiting anaerobic mitochond rial metabolism, the equine nematode, Parascaris equorum, and the cani ne cestode, Dipylidium caninum. The P. equorum PDC yielded 7 major ban ds when separated by SDS-PAGE. The bands of 72, 55-53.5, 41 and 36 kDa corresponded to E2, E3, and E1 alpha and E1 beta, respectively. The c omplex also contained additional unidentified proteins of 43 and 45 kD a. Incubation of the complex with [2-C-14]pyruvate resulted in the ace tylation of only E2. These results suggest that the P. equorum PDC lac ks protein X and exhibits an altered subunit composition, as has been described previously for the PDC of the related nematode, Ascaris suum . In contrast, the D. caninum PDC yielded only four major bands after SDS-PAGE of 59, 58, 39 and 34 kDa, which corresponded to E3, E2, E1 al pha and E1 beta, respectively. Incubation of the D. caninum complex wi th [2-C-14]pyruvate resulted in the acetylation of E2 and a second pro tein which comigrated with E3, suggesting that the D. caninum complex contained protein X and had a subunit composition similar to PDCs from other eukaryotic organisms. Both helminth complexes appeared less sen sitive to inhibition by elevated NADH/NAD(+) ratios than complexes iso lated from aerobic organisms, as would be predicted for PDCs from orga nisms exploiting microaerobic habitats. These results suggest that alt hough these helminths have similar anaerobic mitochondrial pathways, t hey contain significantly different PDCs.