INTERACTION OF MEBENDAZOLE WITH TUBULIN FROM BODY-WALL MUSCLE, INTESTINE, AND REPRODUCTIVE-SYSTEM OF ASCARIS-SUUM

The binding of tritiated mebendazole, a benzimidazole anthelmintic, to tubulin derived from intestine, body wall muscle. and reproductive sy stem of adult Ascaris suum was examined and compared. Mebendazole bind ing was resolved into specific and nonspecific binding and the binding affinity (K-a) and maximum binding at infinite ligand concentration ( B-max)determined. Electron microscopy was performed to assess the tubu lin in various tissues of A. suum quantitatively by observing the pres ence of microtubules. Total binding was highest in intestine followed by body wall muscle. It was least in the reproductive system. The inte stine demonstrated greater specific binding per milligram of protein t han the body wall muscle. However, in the reproductive system extract, high affinity binding was not detected. After correction for nonspeci fic binding of ligand, the results indicated that the B-max of mebenda zole for the tubulin of A, suum intestine was about 3-fold higher than for that of body wall muscle. The K-a of mebendazole for intestinal t ubulin was similar to that for body wall muscle. Electron microscopy o f A. suum tissues demonstrated that the tubulin content decreased from the intestine through the body wall muscle to the reproductive system . Differences in tubulin content from different tissues may determine the selective sensitivity of these tissues to benzimidazole attack.