<b>BINDING AND CONTRACTION-INDUCING ACTIVITY OF MOTILIN </b><b>ANALOGUES </b>

Abstract

We have previously shown the motilin-binding activity in the rabbit and human antral and duodenal smooth muscle. In the present paper, we describe our further studies on the binding and contraction-inducing activity of two analogues of canine motilin (ca-motilin) and several fragments of porcine motilin (po-motilin). The ability to inhibit the membrane binding of po-motilin and to induce the duodenal contraction was markedly reduced in lys1- and ser1-ca-motilin. The N-terminal fragment (1-5) of motilin poorly inhibited the po-binding, and induced a weak contraction at 1 μM. The C-terminal fragment (17-22) did not exert any inhibition on po-motilin binding and did not cause any contraction. Fragments po-(1-11) and (7-22) inhibited the po-motilin binding only slightly, and po-(12-22) did not cause any inhibition. It appears that in addition to the N-terminal portion of motilin, the residue beyond position 14 is also required to form the active site of this molecule.