The binding of closantel to ovine serum albumin, and homogenate fractions of Haemonchus contortus

Closantel binds to the serum proteins of the host and affects blood sucking parasites when they ingest the brood of treated hosts. Closantel binds spe cifically to ovine serum albumin (K-a of 9.3 x 10(6)M(-1)) at site I, the w arfarin/phenylbutazone binding site of albumin Closantel also binds to inve rtebrate haemocyanin and haemolymph. The strongest binding of closantel in homogenates of H. contortus is found in fractions containing soluble protei ns. This binding is of low affinity and, because the site itself is not ful ly denaturable, it may not be proteinaceous. There is no detectable differe nce in binding affinity between homogenate fractions from closantel suscept ible and resistant isolates of adult or larval worms suggesting that closan tel resistance is not due to changes in the closantel receptor or carrier. (C) 2000 Australian Society for Parasitology Inc. Published by Elsevier Sci ence Ltd. All rights reserved.