IDENTIFICATION OF A NOVEL DIHYDROLIPOYL DEHYDROGENASE-BINDING PROTEININ THE PYRUVATE-DEHYDROGENASE COMPLEX OF THE ANAEROBIC PARASITIC NEMATODE, ASCARIS-SUUM

A novel dihydrolipoyl dehydrogenase-binding protein (E3BP) which lacks an amino-terminal lipoyl domain, p45, has been identified in the pyru vate dehydrogenase complex (PDC) of the adult parasitic nematode, Asca ris suum, Sequence at the amino terminus of p45 exhibited significant similarity with internal E3-binding domains of dihydrolipoyl transacet ylase (E2) and E3BP. Dissociation and resolution of a pyruvate dehydro genase-depleted adult A, suum PDC in guanidine hydrochloride resulted in two E3-depleted E2 core preparations which were either enriched or substantially depleted of p45, Following reconstitution, the p45-enric hed E2 core exhibited enhanced E3 binding, whereas, the p45-depleted E 2 core exhibited dramatically reduced E3 binding. Reconstitution of ei ther the bovine kidney or A. suum PDCs with the A. suum E3 suggested t hat the ascarid E3 was more sensitive to NADH inhibition when bound to the bovine kidney core. The expression of p45 was developmentally reg ulated and p45 was most abundant in anaerobic muscle, In contrast, E3s isolated from anaerobic muscle or aerobic second-stage larvae were id entical. These results suggest that during the transition to anaerobic metabolism, E3 remains unchanged, but it appears that a novel E3BP, p 45, is expressed which may help to maintain the activity of the PDC in the face of the elevated intramitochondrial NADH/NAD(+) ratios associ ated with anaerobiosis.