Small Peptides with Physiological Activity

What are some biological functions of small peptides  

FIGURE 3.11 Structures of camosine and its component amino acid /3-alanine. 

Why Are Amino Acids Featured in Health Food Stores  

Amino acids have biological functions other than as parts of proteins and oligopeptides. The following examples illustrate some of these functions for a few of the amino acids. 

Some products sold in health food stores feature the presence of the branched-chain amino acids isoleucine, leucine, and valine. These are essential amino acids in the sense that the body cannot synthesize them. Under normal circumstances, a diet with adequate protein intake provides enough of all the essential amino acids. Athletes involved in intensive training want to prevent muscle loss and to increase muscle mass. As a result, they take protein supplements and pay particular attention to branched-chain amino acids. (These three amino acids are by no means the only essential ones, but they are mentioned specifically here.) 

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Processing of GH could go further, with production of relatively small peptides which retain substantial or even enhanced activity, and it has been suggested that this may be important in the actions of the hormone in vivo [131]. In particular, fragments which retain the diabetogenic or insulin-like activities of GH have been reported [95,131]. What role these play in the normal physiological actions of the hormone is unclear. 

TAP are small peptides that are released when trypsinogen is activated to trypsin. Under physiologic conditions, trypsinogen activation occurs in the intestinal lumen and is mediated by enteropeptidase. Within the intestinal brush border membranes, TAP is quickly degraded by peptidases. In AP, trypsinogen is prematurely activated within pancreatic acinar cells, and TAP is released into the peripheral circulation and potentially can be detected in serum and urine (Saez et al., 2005). Significant increases in plasma and/ or urine TAP concentrations have been reported in fehne, canine, and human patients with AP (Johnson et al., 2004). In humans, there is enough data in the hterature to show... 

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