Isolation of an acid fraction from a fish protein hydrolysate with a calcitonin-gene-related-peptide-like biological activity

The possibility of obtaining calcitonin and/or calcitonin-gene-related pept ide (CGRP) immunorelated molecules from partly digested proteins was invest igated with fish and shrimp hydrolysates. These two peptides were quantifie d by both radioimmunoassay and radioreceptor assay; the positive extracts w ere partly purified. Different hydrolysates were analysed: cod head, stomac h and viscera hydrolysates, a shrimp hydrolysate and two sardine hydrolysat es. Although each cod extract interacted in the CGRP radioimmunoassay, none of these extracts was able to displace the CT binding to its antibody. In contrast, shrimp and sardine hydrolysates interacted with both radioimmunoa ssays, Radioreceptor assays performed on the same extracts demonstrated tha t only three extracts contained the structural determinants that allowed th em to interact in the CGRP radioreceptor assay. No interaction with the cal citonin radioreceptor assay could be demonstrated. Molecular sieving of the two sardine extracts showed that the immunoreactivity was resolved into tw o main fractions, The higher-molecular-mass fraction interacted only in the CG RP radioreceptor assay. The results obtained suggest the presence of a biologically related CGRP molecule in peptone hydrolysates and requires fur ther investigation into the role of these peptide fragments in the regulati on of intestinal function by partly digested proteins.