Resynthesis, enzymatic protein

Figure 2. A process of enzymatic protein degradation and resynthesis for producing a plastein with improved acceptability and an improved amino acid composition (11)...

Enzymatic Protein Degradation and Resynthesis for Protein Improvement... 

Therefore, a combined process of enzymatic protein degradation and resynthesis might be useful in improving both the acceptability and the nutritive values of food proteins at the same time. To carry out the process we have been using in most cases the well-defined proteases, pepsin (EC 3.4.4.1), a-chymotrypsin (EC 3.4.4.5), and papain (EC 3.4.4.10). Our subsequent discussion will therefore center on the three enzymes and their applications to protein degradation and resynthesis. Our use of the word resynthesis refers only to formation of peptide bonds without reference to molecular size of the final product. 

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]. 

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]. 

Fujimaki M, Arai S, Yamashita M. Enzymatic protein degradation and resynthesis for protein improvement. Adv Chem Ser 1977 160 156-184. 

The plastein reaction usually involves two steps hydrolysis of protein and resynthesis of peptide links. Yamashita et al. (20) found similar BV, digestibility, and weight gain for denatured soy meal and soy plastein. This same group (49,50) had described a one-step process by which amino acids may 5 enzymatically incorporated in intact protein to improve protein quality. With soy protein they applied a racemic mixture of D,L-methionine ethyl ester and were able to enzymatically incorporate L-methionine. As Schwimmer (51) has pointed out, one expects the methionine so incorporated to be highly available due to its location at the end of the polypeptide chains. 

Protein Hydrolysates. Instead of ethyl hippurate, a peptic hydrolysate of ovalbumin was used as substrate for the resynthesis reaction (64). This substrate (300 mg) was dissolved in water, adjusted to pH 6.0 with NaOH and to 0.9 ml with additional water. An amino acid ester was added to produce a 22.2mM solution and the mixture preincubated at 37°C for 15 min. Papain (3 mg), dissolved in 0.1M L-cysteine (0.1 ml), was combined with the above-mentioned preincubation mixture and incubation carried out at 37°C. After 2 hr, 0.1N NaOH (10 ml) was added to stop the enzymatic reaction and the resulting solution allowed to stand for 3 hr to hydrolyze completely the remaining amino acid ester as well as the ester group from the peptide product. The free amino acid produced from the base-catalyzed hydrolysis of the amino acid ester was determined with an amino acid analyzer. The amount of the amino acid incorporated was obtained by subtracting the determined value from the initial concentration of amino acid ester. The data obtained with the same L-amino acid esters as used in the model experiment (above) are plotted along the ordinate of Figure 3. An excellent correlation is found between the data from the model experiment and those from this experiment using a protein hydrolysate. In Table III data are shown for the extent of covalent incorporation after 2 hr of various amino acid ethyl esters into the protein hydrolysate. There is a close relationship between... 

Improvement of Solubility of Soybean Protein. Denatured soybean protein is relatively insoluble in aqueous media, which is a disadvantage in processing this protein. This problem might be solved by incorporating a large amount of certain hydrophilic amino acid into soybean protein through its enzymatic degradation and resynthesis. Yamashita et al. (73,... 

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