Structure of somatostatin isolated from bovine retina

Somatostatin-like immunoreactivity (SLI) from bovine retina was purified and its structure determined. Retinal tissue (1868 g) extracted with 3% acetic acid yielded 18.6 nmol SLI. This peptide was purified by chromatography on an affinity column made with anti-somatostatin antiserum, a reverse-phase C-18 HPLC column, and three sequential applications on a reverse-phase phenyl HPLC column. The peptide was purified 103,000-fold from the initial extract with an overall yield of 14.4%. Amino acid sequence determination by an automatic Edman degradation technique revealed the sequence to be as follows: Ser-Ala-Asn-Ser-Asn-Pro-Ala-Met- Ala-Pro-Arg-Glu-Arg-Lys-Ala-Gly-(Cys)-Lys- Asn-Phe-Phe-Trp-Lys-Thr-(Phe, Thr, Ser, Cys). The apparent identity of this peptide with somatostatin octacosapeptide (S28) purified from other mammalian tissue indicates the phylogenetic conservation of its structure and facilitates the use of the retina as a model system for studying the neurotransmitter function of somatostatin.