27.33Somatostatin is a tetradecapeptide and so is composed of 14 amino acids. The fact that Edmandegradation gave the PTH derivative of alanine identifes this as the N-terminal amino acid.A major piece of information is the amino acid sequence of a hexapeptide obtained by partialhydrolysis:Ala-Gly-Cys-Lys-Asn-PheUsing this as a starting point and searching for overlaps with the other hydrolysis products gives theentire sequence.Ala-Gly-Cys-Lys-Asn-PheAsn-Phe-Phe-Trp-LysPhe-TrpLys-Thr-PheThr-Phe-Thr-Ser-CysThr-Ser-CysAla-Gly-Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-Cys1234567891011121314The disulfde bridge in somatostatin is between cysteine 3 and cysteine 14. Thus, the primary struc-ture is27.34It is the C-terminal amino acid that is anchored to the solid support in the preparation of peptidesby the Merrifeld method. Refer to the structure of oxytocin in Figure 27.8 of the text and note thatoxytocin, in fact, has no free carboxyl groups; all the acyl groups of oxytocin appear as amide
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