Abstract
In order for the intestinal mucosa to absorb dietary proteins they have to be digested into single amino acids or very short peptides of a length of not more than four amino acids. In order to study the efficiency of the digestive endopeptidases to digest folded proteins we have analyzed several target proteins under different conditions, native proteins, heat denatured and acid treated. The three pancreatic serine proteases, trypsin, chymotrypsin, and pancreatic elastase, were found to be remarkable inefficient in cleaving native folded proteins whereas pepsin, which acts at a very low pH (pH1.2) was much more efficient, possibly due to the denaturing conditions and thereby better accessibility to internal cleavage sites at the low pH. Heat treatment improved the cleavage considerably by all three pancreatic enzymes, but acid treatment followed by return to neutral pH did not have any major effect. Cleavage at the low pH when the protein is in a denatured state, is apparently very efficient. This indicates that pepsin is the prime enzyme cleaving the properly folded native proteins and that the pancreatic enzymes primarily are involved in generating single amino acids or very short peptides for efficient uptake by the intestinal mucosa.
Highlights
To efficiently use proteins as a food source they have to be transformed into single amino acids or very short peptides of a length of not more than four amino acids
This indicates that pepsin is the prime enzyme cleaving the properly folded native proteins and that the pancreatic enzymes primarily are involved in generating single amino acids or very short peptides for efficient uptake by the intestinal mucosa
Pepsin and the cleavage at low pH seemed to be extremely efficient in the digestion of both linear and tightly folded structures (Figure 1)
Summary
To efficiently use proteins as a food source they have to be transformed into single amino acids or very short peptides of a length of not more than four amino acids. This is performed by a number of different proteases of our digestive system. The hydrochloric acid released by the acid glands of the stomach lowers the pH to below two The protease of this intestinal compartment is pepsin, an aspartic protease with a pH optimum of between pH 1 and 2, and optimized for the environment in the stomach (Janiak 2016; Kageyama 2002). There are several carboxypeptidases that cleave at the carboxy terminal end of the proteins
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