Abbreviations:CD 280synthesis is probably the way to go, since the good properties of each technology can be synergistically used in the context of one process objective.Peptides are heteropolymers composed by amino acid residues linked by peptidic bonds between the carboxyl group of one amino acid residue and the α-amino group of the next one. The definition is rather vague in terms of chain length, peptides ranging from two to a few dozens residues. Its lower limit of molecular mass has been set rather arbitrarily in 6000 Da; molecules larger than that are considered proteins. Peptides are molecules of paramount importance in several fields, especially in health care and nutrition. The case of the hormone insulin (51 residues, 5773 Da) and the non-caloric sweetener aspartame (a dipeptide of aspartic acid and esterified phenylalanine) are relevant examples of those fields of application and the range of molecular size. Medium to small size peptides are, however, the most relevant for such applications.

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In this paper we study the effect of different water-immiscible organic solvents (benzene, toluene, 1-butanol, 1-octanol, dichloroethane, dichloromethane, diethyl ether, hexane, chlorobenzene, acetophenone, n-dodecane, trichloroethylene, ethyl acetate) on the stability (residual caseinolytic activity after 4 h) of soluble phytoproteases, such as araujiain, funastrain and papain in aqueous-organic biphasic systems. Besides, the effect of organic solvents on enzymatic catalysis was quantitatively studied by means of linear free energy relationships (LFERs). The organic solvents were characterized by several physicochemical properties, and multiple linear regression analysis (MLRA) together with non-linear regression were the methods used to search the relationships between the residual caseinolytic activity data and several physicochemical parameters. Those enzymes show much greater activity and stability in some biphasic media than in water. On the other hand, all developed correlations represented highly significant LFERs models and showed that non-specific polar and hydrophobic factors are of prime and approximately equal importance for the biocatalytic activity of araujiain, funastrain and papain in the studied biphasic systems, while the specific polar interactions are of little importance for activity. The results suggested that araujiain, funastrain and papain do not suffer unfolding in the studied biphasic media and they are able to retain their native or native-like configurations, though with altered characteristics or properties. This fact was demonstrated by means of a comparative FTIR spectroscopy study in both, buffer and biphasic media, for each studied enzyme.

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