Digestibility, protein, effect residues

Changes in the number of free amino residues alter the modified proteins susceptibility to proteolysis. Albumin chlorination and /V-chloramine formation decreases susceptibility to trypsin digestion. Removing of chloramine residues by treatment with thiosulfate shows that chlorination alters albumin properties by a biphasic mode the reversible chlorination and removal of chloramine moieties markedly increases albumin susceptibility to proteolysis, whereas chlorination produces the irreversible loss of amino moieties and carbonyl group formation effects decrease in albumin susceptibility to trypsin digestion. The effect is related to the number of lost amino residues. A similar relationship was observed for IgG. Fibrinogen and protamine, on the other hand, did not show dependence between chlorination and proneness to trypsin proteolysis (06). 

The ability to identify and quantify cyanobacterial toxins in animal and human clinical material following (suspected) intoxications or illnesses associated with contact with toxic cyanobacteria is an increasing requirement. The recoveries of anatoxin-a from animal stomach material and of microcystins from sheep rumen contents are relatively straightforward. However, the recovery of microcystin from liver and tissue samples cannot be expected to be complete without the application of proteolytic digestion and extraction procedures. This is likely because microcystins bind covalently to a cysteine residue in protein phosphatase. Unless an effective procedure is applied for the extraction of covalently bound microcystins (and nodiilarins), then a negative result in analysis cannot be taken to indicate the absence of toxins in clinical specimens. Furthermore, any positive result may be an underestimate of the true amount of microcystin in the material and would only represent free toxin, not bound to the protein phosphatases. Optimized procedures for the extraction of bound microcystins and nodiilarins from organ and tissue samples are needed. 

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.)...

The enzymes used for this type of digestion in Analytical Chemistry are mainly hydrolytic enzymes, the catalytic effect of which is based on the insertion of water at a specific bond of the substrate. The hydrolytic enzymes used in analytical applications include lipases (which hydrolyse fats into long-chain fatty acids and glycerol) amylases (which hydrolyse starch and glycogen to maltose and to residual polysaccharides) and proteases (which attack the peptide bonds of proteins and peptides themselves). 

Enzymes, we have said, are proteins that act as enormously effective catalysts for biological reactions. To get some idea of how they work, let us examine the action of just one chymotrypsin, a digestive enzyme whose job is to promote hydrolysis of certain peptide links in proteins. The sequence of the 245 amino acid residues in chymotrypsin has been determined and, through x-ray analysis, the conformation of the molecule is known (Fig. 37.1). It is, like all enzymes, a soluble globular protein coiled in the way that turns its hydrophobic parts inward, away from water, and that permits maximum intramolecular hydrogen bonding. 

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