An elasmobranchian somatostatin: primary structure and tissue distribution in Torpedo marmorata.

Extracts of brain, stomach, pancreas, and intestine from Torpedo marmorata, an elasmobranchian cartilaginous fish, contained somatostatin-like immunoreactivity. Gel filtration studies demonstrated that material with the elution volume of somatostatin-14 was the only component detected in all tissue extracts. This result contrasts with the situation in mammals where prosomatostatin is processed to multiple molecular forms in a tissue-specific manner. Somatostatin from pancreas and gut was purified to homogeneity and amino acid sequence analysis indicated that T. marmorata somatostatin from both tissues has the same structure as somatostatin-14 isolated from the higher vertebrates. Further examination of other lower vertebrate species is required in order to test the hypothesis that the ability to regulate the production of multiple forms of a regulatory peptide from a single precursor molecule developed only relatively late in evolution.