Proteases, protein digestion

ProSwift WAX IS can be used to separate complex protein mixtures such as pancreatin, which contains a variety of proteases (protein digesting enzymes such as trypsin or pepsin), amylases (carbohydrate digesting enzymes), and lipases (fat digesting enzymes). Figure 3.287 shows the separation of pancreatin on a 50 mm x 1 mm i.d. ProSwift WAX-IS into an unbound and a bound fraction, the latter one containing several well-resolved peaks. 

Pancreatic secretion for many, if not most, species is regulated in order to insure adequate protein digestion. Correspondingly, protease inhibitors have a greater impact on pancreatic secretion than do inhibitors of amylase and lipase (Toskes, 1986). The secretory response of the exocrine pancreas to protease inhibitors can be rapid (< 10 min), does not involve parallel increases in the secretion of all enzymes (Holm et al., 1992), and is probably mediated by a signaling pathway (see below). 

Protease Vegetable proteins Increased protein digestibility Reduced nitrogen excretion... 

Exocrine pancreatic insufficiency is most commonly caused by cystic fibrosis, chronic pancreatitis, or pancreatic resection. When secretion of pancreatic enzymes falls below 10% of normal, fat and protein digestion is impaired and can lead to steatorrhea, azotorrhea, vitamin malabsorption, and weight loss. Pancreatic enzyme supplements, which contain a mixture of amylase, lipase, and proteases, are the mainstay of treatment for pancreatic enzyme insufficiency. Two major types of preparations in use are pancreatin and pancrelipase. Pancreatin is an alcohol-derived extract of hog pancreas with relatively low concentrations of lipase and proteolytic enzymes, whereas pancrelipase is an enriched preparation. On a per-weight basis, pancrelipase has approximately 12 times the lipolytic activity and more than 4 times the proteolytic activity of pancreatin. Consequently, pancreatin is no longer in common clinical use. Only pancrelipase is discussed here. 

Enzyme assays As shown previously the LMW fraction had a repressing effect on the protein digestion in the in vivo experi-ment. Accordingly, it was of interest to study in vitro the effect of this fraction on the kinetics of reactions catalyzed by proteases and peptidases present in the gastro-intestinal tract. 

What is the fate of the proteases after protein digestion ... 

Since keratinase is a versatile protease that digests all kinds of proteins, it is possible that supplementation of the enzyme in feed may improve the feed digestibility. In 2001 keratinase was tested as a feed additive. The first test in young chicks was positive, and reproduced by many more experiments 0.1% of crude keratinase in a regular corn-soy diet improved the body weight gain, the feed conversion ratio (FCR), or feed efficiency in broiler chickens. Numerous experiments included the cage tests of chicks to 3-4 weeks of age (Odetellah et al., 2003), pen trials on a research farm to 6 week market age (Odetellah et al, 2005), and the commercial tests conducted by private com-... 

There is a report that in pea embryo, some of the SSSs may also be bound to the starch granule (Denyer et al., 1993) and that in maize endosperm, some of SSSI adheres to the starch granule (Mu et al., 1994). The conclusions in the pea embryo study (Denyer et al., 1993) are based on positive immunoblots obtained after electrophoresis of the SSS with antibody prepared against the GBSS, and also on the similarity of the amino-acid sequence of three peptides obtained from protease SV8 digests of the SSS. This clearly shows there is a close relationship between SSSII and GBSSII, but does not indicate that they are identical proteins. It is also... 

Dietary proteins, with very few exceptions, are not absorbed rather they must be digested into amino acids, or di- and tripeptides. Protein digestion begins in the stomach, where proenzyme pepsinogen is autocatalytically converted to pepsin A. Most proteolysis takes place in the duodenum via enzymes secreted by the pancreas, including trypsinogen, chymotrypsinogen and pro-carboxypeptidase A. These serine and zinc proteases are produced in the form of their respective proenzymes they are both endopeptidase and exopeptidase, and their combined action leads to the production of amino acids, dipeptides and tripeptides. 

Hydrolysis of proteins without taste by proteases often produces bitter peptides. Hydrophobic amino acid residues located in the interior of protein molecules in aqueous solution are exposed by fragmentation of the protein molecules treated with proteases, and the peptides containing a number of hydrophobic amino acid residues occur in the solution (13). Many bitter peptides as shovm in Table 4-have been isolated from protein digests with proteinases (14-22). 

Since the importance of dietary protein for human health and nutrition has long been recognized, it is surprising that remarkably little is known about the physiological processes involved in protein digestion. Many proteases—enzymes catalyzing the hydrolysis of peptide bonds—... 

Protein digestion begins in the stomach, where the acidic environment favors protein denaturation. Denatured proteins are more accessible as substrates for proteolysis than are native proteins. The primary proteolytic enzyme of the stomach is pepsin, a nonspecific protease that, remarkably, is maximally active at pH 2. Thus, pepsin can be active in the highly acidic environment of the stomach, even though other proteins undergo denaturation there. 

The principles of fluorescence quenching have been successfully applied to assays for protease activity. Proteases are digestive enzymes that degrade polypeptides into smaller oligopeptides or constituent amino acids. A general assay12 for protease activity employs a substrate prepared by covalently derivatizing a protein, transferrin, with a number of fluorescein isothiocyanate (FITC) labels. The FITC labeled proteins (Fig. 3.3) exhibit absorbance maxima at 495 nm and emission maxima at 525 nm. 

By contrast, beneath a healthy gingival sulcus, there is an intermittent flow of proteins from serum, blood plasma proteins in which clotting has been inactivated (Sect. 11.4.1). This exudate of serum proteins, the gingival crevicular fluid (GCF), provides a sulcus that is richer in proteins than saliva and an environment that is more suited for an asaccharo-lytic microbiota (Sect. 13.1.2). Asaccharolytic bacteria secrete proteases that digest proteins to small peptides, which they digest (ferment) in the cytosol. 

---