Prosomatostatin-I is processed to somatostatin-26 and somatostatin-14 in the pancreas of the bowfin, Amia calva

With the exception of the Agnatha (lampreys and hagfishes), somatostatin-14 is the predominant molecular form of somatostatin in the pancreas of species from all classes of vertebrates yet studied. The pancreas of the holostean fish, Amia calva (bowfin; order Amiiformes) contained somatostatin-like immunoreactivity that was resolved by reversed phase HPLC in two components. The primary structure of the more abundant peptide (somatostatin-26) was established as: Ser-Ala-Asn-Pro-Ala⁵-Leu-Ala-Pro-Arg-Glu¹⁰-Arg-Lys-Ala-Gly-Cys¹⁵-Lys-Asn-Phe-Phe-Trp²⁰-Lys-Thr-Phe-Thr-Ser²⁵-Cys. This amino acid sequence shows one substitution (Leu for Met at position 6) and two deletions compared with mammalian somatostatin-28. The minor component was identical to somatostatin-14. The data show that the pathway of post-translational processing of prosomatostatin-I in the bowfin pancreas is appreciably different from the corresponding pathway in teleost fish and higher vertebrates.