Gastrin Amino acid sequence

Two attempts have been reported to predict the conformation of a polypeptide hormone by assembling the appropriate residues in their predicted conformation (63, 90). In this manner, the amino acid sequence of bradykinin was predicted to exist in a random coil conformation, with variation around the glycine bond, and with no interaction predicted between phenyl groups. As yet no experimental evidence confirms this prediction however, existing experimental evidence suggests that the prediction is reasonable (67-69). In the second study the conformation of gastrin tetrapeptide was predicted (90). 

Gl. Gantz, I., Takiuchi, P., and Yamada, T., Cloning of canine gastrin cDNA encoding variant amino acid sequences. Digestion 46, Suppl. 2, 99-104 (1990). 

Discovery of gastrin, the continued doubt about its existence were mentioned in the introductory part of this chapter. These doubts were laid to rest with the isolation of the hormone, determination of its amino acid sequence and synthesis. Gastrin is an acidic 17-peptide with pyroglutamic acid at the N-terminus and with not less than five glutamic acid residues, in a row, in its chain. Two variants were isolated, (porcine) gastrin I... 

Fig. 4-3. Amino acid sequences of the gastrin peptides. Pyro=pyroglutamyl R = H or SO3H...

Since then, secretin has been purified and found to be a strongly basic polypeptide hormone (mol wt 5,000) composed of 27 amino acids. Its amino acid sequence resembles that of gastrin and includes 4 argine units. A specific enzyme (secretinase) in blood seems to be capable of hydrolyzing secretin selectively. 

Recent work on gastrin, the peptide which stimulates production of gastric acid and pwc atic enzymes, has been covered in two conferences 33 13 and two reviews. 5,13° Amino acid sequences are known for the human, porcine, bovine (the same as ovine),, 139 and feline 1 hormones. 

Caerulein is a decapeptide isolated from the skin of the Aus-straliaifrog Hyla caerulea (l). The determination of the amino-acid sequence and subsequent synthesis have been carried out in these laboratories (2). According to Erspamer et al. (3) this pe tide causes a long-lasting blood pressure fall and has gastrin and pancreozymin-like activities on gall bladder motility and on gastric and pancreatic secretions. In the dog, caerulein stimulates external pancreatic secretion at doses as low as 3-6 ng/kg i. v. and decreases blood pressure at doses of 10-100 ng/kg i. v. 

End group analysis shows that the C-terminal and N-terminal amino acids are Phe and Glu, respectively. Hydrolysis with chymotrypsm yields the following four peptides. Write two possible amino acid sequences of feline gastrin. 

Somatostatin, a 14-amino-acid peptide, is found in the hypothalamus and other parts of the central nervous system. It has been sequenced (Figure 37-1) and synthesized. It inhibits growth hormone release in normal individuals. Somatostatin has also been identified in the pancreas and other sites in the gastrointestinal tract. It has been shown to inhibit the release of glucagon, insulin, and gastrin. 

Jn Figure 2.1U, examine the order of ainiriD adds at the C termiivi of gastrin and cholecystokin. How many amino acids are identical in the two hormones Are any other identical sequences shared by these hormones Ihcsc questions are relevant lo the concept that a number of hormones with different functions are actually part of the same family of hormones. A number of proteins, such as various enzymes, hormone receptor proteins, and DNA-binding protcirLS, also share similar primary sequences and thus may becortsidered members of specific families of proteins. 

Long before gastrin was identified, peptide chemists had agreed to number the amino acids in a peptide sequence beginning at the N-terminal amino acid. Follow-... 

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