Abstract
Dietary proteins are known to contain bioactive peptides that are released during digestion. Endogenous proteins secreted into the gastrointestinal tract represent a quantitatively greater supply of protein to the gut lumen than those of dietary origin. Many of these endogenous proteins are digested in the gastrointestinal tract but the possibility that these are also a source of bioactive peptides has not been considered. An in silico prediction method was used to test if bioactive peptides could be derived from the gastrointestinal digestion of gut endogenous proteins. Twenty six gut endogenous proteins and seven dietary proteins were evaluated. The peptides present after gastric and intestinal digestion were predicted based on the amino acid sequence of the proteins and the known specificities of the major gastrointestinal proteases. The predicted resultant peptides possessing amino acid sequences identical to those of known bioactive peptides were identified. After gastrointestinal digestion (based on the in silico simulation), the total number of bioactive peptides predicted to be released ranged from 1 (gliadin) to 55 (myosin) for the selected dietary proteins and from 1 (secretin) to 39 (mucin-5AC) for the selected gut endogenous proteins. Within the intact proteins and after simulated gastrointestinal digestion, angiotensin converting enzyme (ACE)-inhibitory peptide sequences were the most frequently observed in both the dietary and endogenous proteins. Among the dietary proteins, after in silico simulated gastrointestinal digestion, myosin was found to have the highest number of ACE-inhibitory peptide sequences (49 peptides), while for the gut endogenous proteins, mucin-5AC had the greatest number of ACE-inhibitory peptide sequences (38 peptides). Gut endogenous proteins may be an important source of bioactive peptides in the gut particularly since gut endogenous proteins represent a quantitatively large and consistent source of protein.
Highlights
The main role of dietary proteins is to provide amino acids for body protein synthesis [1]
A prediction of the number of bioactive peptides that would be released from gut endogenous proteins and dietary proteins after upper gastrointestinal tract digestion was made using an in silico simulation based on the amino acid sequence of the proteins and the reported specificity of the major proteases present in the gastrointestinal tract
The total where, ao is the total number of identified bioactive peptides present in the protein or the number of bioactive peptides with a specific activity based on the BIOPEP database [22], N is the total number of amino acid residues within the protein
Summary
The main role of dietary proteins is to provide amino acids for body protein synthesis [1]. Investigations over the last two decades have shown that dietary protein can be a source of latent bioactive peptides (from 2 to greater than 40 amino acids long) that when released during digestion in the gastrointestinal tract can act as modulators of various physiological functions [2,3,4]. These peptides are reported to possess a range of effects including antihypertensive, cholesterol-lowering, antioxidant, anticancer, immunomodulatory, antimicrobial, opioid, antiobesity and mineral binding effects [2,5,6]. A considerable amount of endogenous (non-dietary) protein is present in the lumen of the gastrointestinal tract during digestion, consisting of proteins such as mucins, serum albumin, digestive enzymes, peptide sequences and that the possibility exists that these peptides are released during gastrointestinal digestion
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