Oligopeptide methionine

The kinetics and mechanism of polymerization of IV-carboxy-a-amino acid anhydrides as well as the biological properties of poly-a-amino acids have been studied and reviewed extensively (70,79,80). The critical chain length for helix formation varies from one amino acid to another (81,82). The critical chain length in L-methionine oligopeptides is the heptamer (83). 

The major nutraceutical application of marine-derived bioactive peptides has been ACE inhibition, and a partial list of identified bioactive peptides is given in Table 27.1. Fish protein has been reported to be an advantageous starting material for preparation of ACE inhibitory peptide hydrolysates (Curtis et al., 2002). Marine-derived protein hydrolysate tends to contain high concentrations of cysteine, methionine, and arginine, all of which help reduce hypertension (Kristinsson, 2007). Such marine-derived peptides could be used as potent functional food additives and represent a healthier and natural alternative to ACE inhibitor drugs (Li et aL, 2004). Currently, the bioactive oligopeptides from dried bonito and sardine muscle have been approved as Foods for Specified Health Use by the Ministry of Health and Welfare in Japan. 

Protein digestion begins in the stomach, where protein is denatured by the low pH and is exposed to the action of pepsin. The low pH also provides the optimal H+ concentration for pepsin activity. The zymogen precursor pepsinogen (M.W. 40,000) is secreted by the chief cells and is converted to pepsin (M.W. 32,7(K)) in the acid medium by removal of a peptide consisting of 44 amino acid residues. This endopeptidase hydrolyzes peptide bonds that involve the carboxyl group of aromatic amino acid residues, leucine, methionine, and acidic residues (Table 12-5). The products consist of a mixture of oligopeptides. 

Studies on the uptake of amino acids and oligopeptides into embryos of Hordeum vulgare indicate independent transport systems (97) whilst uptake studies with chloroplasts from Pisum sativum have indicated the presence of two carrier systems, one transporting glycine and aliphatic amino acids (L-alanine, L-leucine, L-isoleucine, and l-valine) and the other transporting L-serine, L-threonine and L-methionine. The carrier systems may not perform active transport but merely facilitated diffussion (244). Other studies have also indicated the possibility of transport of amino acids into chloroplasts (285). 

If methionine is the first amino acid incorporated into an oligopeptide, what oligopeptide is coded for by the following stretch of mRNA ... 

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