Isolation, sequence, and bioactivity of chicken motilin.
Motilin was isolated from acid extracts of the small intestine of chickens by a combination of gel filtration chromatography, ion-exchange, and reverse-phase HPLC. The purification was monitored using a radioreceptor assay. The sequence of chicken motilin is FVPFFTQSDIQKMQEK-ERNKGQ. Although the six residues differing from porcine motilin (4, 7-10, and 12) are mostly in the pharmacophore of porcine motilin, the affinity of chicken motilin and of the (1-14) fragment of chicken motilin for the motilin receptor of rabbit antral smooth muscle is not much reduced (pKds of 8.90 and 8.45), compared with the affinity of [Nle13]porcine motilin (pKd 9.12). With smooth muscle tissue of the chicken, however, receptors could not be demonstrated with binding studies. In the tissue bath chicken motilin induced a dose-dependent tonic contraction, which was most pronounced with muscle strips prepared from chicken jejunum. This response was blocked by the Ca2+ antagonist verapamil, but atropine, TTX, L-NNA, guanethidine, prazosin, and yohimbine had no effect. The pEC50 for chicken motilin in the chicken jejunum was 7.41. Motilins from other species had lower potencies, and [Phe3, Leu13]porcine motilin, an antagonist in the rabbit, was an agonist in the chicken. The motilin agonists erythromycin A and EM-523 were almost without effect. Tested against rabbit duodenum, chicken motilin had a smaller potency than mammalian motilins. Thus, chicken motilin and the chicken motilin receptor differ from their mammalian counterparts.
De Clercq
P
P
Gut Hormone Laboratory, K.U.L., Leuven, Belgium.
Depoortere
I
I
Macielag
M
M
Vandermeers
A
A
Vandermeers-Piret
M C
MC
Peeters
T L
TL
D000595:Amino Acid Sequence; D000818:Animals; D002645:Chickens; D007422:Intestines / Q000737:chemistry; D007700:Kinetics; D008969:Molecular Sequence Data; D009037:Motilin / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D011817:Rabbits; D011964:Receptors, Gastrointestinal Hormone / Q000378:metabolism; D018013:Receptors, Neuropeptide / Q000378:metabolism; D013552:Swine; D014700:Verapamil / Q000494:pharmacology
D011964:Receptors, Gastrointestinal Hormone; D018013:Receptors, Neuropeptide; C050802:motilin receptor; D009037:Motilin; D014700:Verapamil