Proteins enzymatic hydrolysis

A Tokyo group [46] was the first to propose a combined process of enzymatic protein hydrolysis and resynthesis for producing a product with improved sensory properties and modified amino acid composition. An enzymatic reaction was used also for the removal of bound impurities [108,109], for debittering of hydrolysates [47,110], and for decolorization of proteins of particular origin [111]. 

An excellent review on protein hydrolysis for amino acid composition analysis has been published by Eountoulakis and Lahm [190], Hydrolysis can be performed by either chemical (under either acidic or basic conditions) or enzymatic means. The acidic hydrolysis itself can be carried out in a liquid or a gas-phase mode. The conventional acid hydrolysis uses 6M HCl for 20-24 h at 110°C under vacuum [200], In these conditions, asparagine and glutamine are completely hydrolyzed to aspartic acid and glutamic acid, respectively. Tryptophan is completely destroyed (particularly in the presence of high concentrations of carbohydrate), while cysteine and sometimes methionine are partially oxidized. Tyrosine, serine, and threonine are partially destroyed or hydrolyzed and correction factors have to be applied for precise quantification [190,201],... 

Sometimes the easiest way to destroy drug-protein binding is to dilute the sample with a physiological saline solution. For instance, for isoxazolyl penicillins with a binding percentage of over 95%, dilution with 9 volumes of 0.9% sodium chloride solution can be sufficient (9). Alternative widely used techniques are based on either protein denaturation or enzymatic/chemical hydrolysis of the drug-protein complexes (10-12). 

Protein hydrolysates are usually produced by limited enzymatic hydrolysis of protein molecules in foodstuff, yielding polypeptides that are smaller in molecular mass. Protein hydrolysis has several aims. The most common is to make the protein moiety of afoodstuff soluble by reducing the size of the peptides. Solubilization simplifies isolation of the protein moiety by physical means. Protein hydrolysis has also been applied to improve the functional, organoleptic, and nutritional value of a foodstuff. Advances in the technology of protein hydrolysate production has allowed the use of unconventional protein sources for animal and human food. 

Protein hydrolysis Water activity Water content Water retention alkaline, 437 enzymatic of p-glucan, 753 olive oil substrate, 373 polysaccharides characteristics of, 728-729 sulfuric acid, 724-727 trifluoroacetic acid (TFA), 721-726, 729-730... 

A 72-h hydrolysis profile of a 10% acetic acid-pretreated softwood substrate (Fig. 1) represents a typical enzymatic cellulose hydrolysis course with the majority of the cellulose (up to 70%) broken down within the first 24 h. However, the conversion of the remaining cellulose ( 30%) was incomplete, even after another 2 d of incubation. The decrease in the hydrolysis rate in the latter phase is likely owing to accumulation of end products. To demonstrate that the end products played a major inhibitory role, we removed the produced sugar from the hydrolysate through ultrafiltration. Fresh buffer was then added to the retained protein and the residual substrate to attain the initial volume, and the hydrolysis was continued under the same condition. As shown in Fig. 1, significant increases in the hydrolysis rate were observed after the sugar removal at both 24 h and 48 h of incubation, with complete hydrolysis attained after 48 h and 60 h of incubation respectively. 

The results on the hydrolysis of partially methylated /3-casein by plasmin indicate that proteins radiomethylated to a low level can serve as substrates for trypsin-like enzymes and probably for proteinases in general. Because it is likely that methylation will interfere with enzymatic attack at lysine residues, the complete hydrolysis of /3-casein probably would not be possible. Studies on mastitic milk demonstrate the usefulness of 14C-methyl proteins for qualitative examination of protein hydrolysis in complex multiprotein systems where resolution and characterization of individual protein fragments is difficult. The requirements in such studies are the availability of pure samples of the proteins under investigation and a suitable technique for separating the radio-labeled protein from hydrolytic products. 

To assess Se distribution and speciation in Brazil and other types of nuts, the defatted and powdered samples were fractionated into proteins and cytosol as shown by a Bow chart in Figure 21.1 [13, 14], For the evaluation of Se binding to proteins by SEC, protein precipitate was solubilized with SDS-containing acetate buffer. For the speciation of low-molecular-weight (LMW) Se compounds released from proteins, two procedures of protein hydrolysis were applied and the results obtained were compared. It was shown that acid hydrolysis with methane-sulfonic acid allowed for more efferent release of selenomethionine from proteins as compared with enzymatic proteolysis [14],... 

Enzymatic assays can be applied in the marine environment to provide indirect information on dissolved compounds that are available to fuel bacterial production. Approaches that have been commonly appHed include measuring hydrolytic enzyme activities in seawater and monitoring degradation rates of model compounds. Protein hydrolysis in seawater is rapid as expressed by model protein studies (e.g., Nunn et al., 2003 Pantoja and Lee, 1999). This rapid and selective removal of dissolved proteins explains the relatively minor contribution from proteins to the accumulating DOM reservoir even though proteins are by far the most abundant intracellular biochemical. In an elegant study, Nunn and coworkers (2003) used matrix assisted laser desorption/ionization (MALDI) time of flight (TOP) mass... 

One striking observation about the reactions catalyzed by RTA and pertussis toxin is that the enzymes appear to use opposite catalytic strategies. The analogous non-enzymatic reactions, hydrolysis of adenosine 5 -monophosphate (AMP) and NAD, both have highly dissociative AnD mechanisms with oxocarbenium ionlike transition states. In the ADP-ribosylation of protein Gid by pertussis toxin, the AnDn mechanism is more synchronous, with more nucleophile participation and lower oxocarbenium ion character than the non-enzymatic reaction. " In contrast, the RTA-catalyzed depurination of RNA" and DNA substrates proceeds through stepwise Dj,j An mechanisms where the enzyme stabilizes an oxocarbenium ion to the point that it becomes a discrete intermediate. This is illustrated with a hypothetical free energy surface for each reaction (Fig. 14). 

Functional properties of food protein are sensitive to changes in the size of the protein molecule, structural conformation, and the level and distribution of ionic charges. They can be modified, both enzymatically and nonenzymatically, by reactions such as protein hydrolysis, denaturation, ionization, and cross-linking. Enzymatic modifications are considered safer for food uses and therefore more desirable. However, many nonenzymatic methods have been proven safe and, because of their simplicity and great effectiveness, they are often the method of choice. Specifically, food proteins have been modi-... 

Enzymatic protein modifications, that is, enzymatic hydrolysis and resynthesis, have been described for improving the functional properties and the nutritive values of food proteins [37,46,123]. 

Second, of several proteases that are known to participate in peptide/protein hydrolysis, the cysteine and aspartic proteases, also known as cathepsins, constitute a majority of the endosomal/lysosomal proteolytic machinery. These enzymes are often synthesized in an inactive form requiring excision of the pro-domain facilitated by other proteases or autocatalytic mechanisms activated by acidic pH. Cathepsins seem to have originally evolved to catabolize both internalized and endogenous proteins crucial for cellular homeostasis, autophagy, apoptosis, and antigen presentation. The optimal pH range for enzymatic activity of cathepsins ranges from 5.0 to 6.5, as is the case with endosomes/lysosomes. 

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