Elastase protein digestion

Protein digestion occurs in two stages endopeptidases catalyse the hydrolysis of peptide bonds within the protein molecule to form peptides, and the peptides are hydrolysed to form the amino acids by exopeptidases and dipeptidases. Enteropeptidase initiates pro-enzyme activation in the small intestine by catalysing the conversion of trypsinogen into trypsin. Trypsin is able to achieve further activation of trypsinogen, i.e. an autocatalytic process, and also activates chymotrypsinogen and pro-elastase, by the selective hydro-... 

Trypsin, chymotrypsin, and elastase are three of the most important protein-digesting enzymes secreted by the pancreas. Despite their similarities they have different substrate specificity, that is, they cleave different peptide bonds during protein digestion. 

Protein digestion continues in the small intestine where the enzymes trypsin, chymotrypsin, elastase, and others catalyze the hydrolysis of peptide bonds at different sites in the protein. For instance, chymotrypsin cleaves peptide bonds on the carbonyl side of aromatic amino acids and trypsin cleaves peptide bonds on the carbonyl side of basic amino acids. Together these proteolytic enzymes degrade large dietary proteins into amino acids that can be absorbed by cells of the small intestine. 

The digestion of proteins begins in the stomach, where the low pH denatures the proteins so that they are more easily hydrolyzed by the enz)une pepsin. They are further degraded in the small intestine by tiypsin, ch)miotiypsin, elastase, and other proteases. The products of protein digestion—amino acids and short oligopeptides—are taken up by the cells lining the intestine. This uptake also involves an active transport mechanism. 

Raw soybeans contain numerous trypsin inhibitors. These compounds block the action of trypsin and other enzymes, such as chymotrypsin, elastase, and other serine proteases, which decreases protein digestibility and bioavailability (Liener, 1994). Trypsin inhibitors can be inactivated by moist heat (Osborne Mendel, 1917), such as extrusion (Alomso et al., 1998). Romarheim et al. (2005) showed that extrusion sufficiently eliminated trypsin inhibitors in SBM-based diets fed to mink (2.7—0.2 mg of trypsin inhibitors/g diet, and 8.3-3.1 mg of trypsin inhibitors/g diet for defatted SBM diet). With similar heating conditions (>116°C) in both extrusion and canning processes, trypsin inhibitors should not be a problem in pet foods. 

The digestive enzymes trypsin, chymotrypsin, elastase, and proteinase E are related serine proteases. All three are synthesized in the pancreas which secretes 5-10 g per day of proteins, mostly the inactive proenzymes (zymogens) of digestive enzymes.191,192... 

In the digestive system trypsin, chymotrypsin, and elastase work as a team. They are all endopeptidases, which means that they cleave protein chains at internal peptide bonds, but each preferentially hydrolyses bonds adjacent to a particular type of amino acid residue (fig. 8.4). Trypsin cuts just next to basic residues (lysine or arginine) chymotrypsin cuts next to aromatic residues (phenylalanine, tyrosine, or tryptophan) elastase is less discriminating but prefers small, hydrophobic residues such as alanine. 

Schematic diagrams of the amino acid sequences of chymotrypsin, trypsin, and elastase. Each circle represents one amino acid. Amino acid residues that are identical in all three proteins are in solid color. The three proteins are of different lengths but have been aligned to maximize the correspondence of the amino acid sequences. All of the sequences are numbered according to the sequence in chymotrypsin. Long connections between nonadjacent residues represent disulfide bonds. Locations of the catalytically important histidine, aspartate, and serine residues are marked. The links that are cleaved to transform the inactive zymogens to the active enzymes are indicated by parenthesis marks. After chymotrypsinogen is cut between residues 15 and 16 by trypsin and is thus transformed into an active protease, it proceeds to digest itself at the additional sites that are indicated these secondary cuts have only minor effects on the enzymes s catalytic activity. (Illustration copyright by Irving Geis. Reprinted by permission.)...

We were also able to use FAB mass spectrometry to determine the amino acid sequence around the active site serine in the acyl transference domain of rabbit mammary fatty acid synthase.6 The synthase was labelled in the acyl transferase domain(s) by the formation of O-ester intermediates after incubation with [" " C]-acetyl- or malonyl-CoA (Fig. 2A). The modified protein was then digested with elastase (Fig. 2B), and radioactive material isolated via successive purification steps on Sephadex G-50 and reverse phase HPLC. The isolated peptides were then sequenced by FAB MS. The data summarized in Table II established the sequences of both the acetyl and malonyl hexapeptides to be N-acyl-Ser-leu-Gly-Glu-Val-Ala. 

The properties and spatial arrangement of the amino acid residues forming the active site of an enzyme will determine which molecules can bind and be substrates for that enzyme. Substrate specificity is often determined by changes in relatively few amino acids in the active site. This is clearly seen in the three digestive enzymes trypsin, chymotrypsin and elastase (see Topic C5). These three enzymes belong to a family of enzymes called the serine proteases - serine because they have a serine residue in the active site that is critically involved in catalysis and proteases because they catalyze the hydrolysis of peptide bonds in proteins. The three enzymes cleave peptide bonds in protein substrates on the carboxyl side of certain amino acid residues. 

Proteolytic enzymes (proteases) are involved in a wide variety of physiological processes including digestion, fertilization, coagulation, and the immune response. Outside of their normal environment, proteases can be extremely destructive and natural human plasma inhibitors inhibit most proteases that escape. Imbalance in protease-protease inhibitor systems can lead to a number of diseases of which pulmonary emphysema is one well-characterized example. This disease results when the protease elastase attacks elas-tin, the major elastic protein in the lung. Considerable effort has been devoted to the synthesis of inhibitors of proteolytic enzymes such as elastase for possible therapeutic use. In the future, specific and selective synthetic protease inhibitors should be useful for treating specific diseases that range from the common cold to chronic disorders such as emphysema. 

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