Heterogeneity of immunoreactive motilin.

Motilin-like immunoreactivities were examined in extracts of duodena of pig, human, dog, rat, cat, rabbit and guinea pig with a combination of radioimmunoassays using three different antisera possessing distinct region-specificities. Antisera GP-1103 and R-1104 were rather C-terminal specific, but the immunological feature of GP-1103 was different from that of R-1104. In the case of antiserum GP-1103, the Glu residue in position 15 in the motilin molecule participated in antigen-antibody interaction, but not in the case of R-1104. Antiserum MBR-02 was N-terminal specific, with of the three assay systems, only a single major peak was detected in the elution profile from BioGel P-10 column of motilin-like immunoreactivity in the porcine duodenal extract, of which the elution volume corresponded to that for synthetic porcine motilin. On the other hand, the gel filtration profiles of the human and canine duodenal extracts consisted of two or three peaks of the immunoreactivity. The major peak emerged in the elution volume identical with that for synthetic porcine motilin and the other two peaks were eluted earlier. The peak which was eluted in the volume corresponding to that for BSA marker was detectable only by the assay system with N-terminal specific antiserum MBR-02. The immunoreactivity of the major peak component in the human, canine or rat extract was found to be lower than that in the porcine extract. The present data may indicate the existence of heterogeneity of motilin-like immunoreactivity and species variation of the structure of the immunoreactive motilin.