Enzymatic cross-linking

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-... 

D Chitosan Cross-linking Enzymatic chitosanase Glucosamines 14,8,22,25,26]... 

E Collagen Cross-linking Enzymatic collagenase or lysozyme Various peptides depending on sequence 18,31-33]... 

In most cases the microspheres were insoluble. The polysaccharides might be partially cross-linked via amido groups formed by the carboxyl groups of the polyanion and the restored free amino group of chitosan. The susceptibility to enzymatic hydrolysis by lysozyme was poor, mainly because lysozyme, a strongly cationic protein, can be inactivated by anionic polysaccharides [207]. 

The multiple emulsion technique includes three steps 1) preparation of a primary oil-in-water emulsion in which the oil dispersed phase is constituted of CH2CI2 and the aqueous continuous phase is a mixture of 2% v/v acetic acid solution methanol (4/1, v/v) containing chitosan (1.6%) and Tween (1.6, w/v) 2) multiple emulsion formation with mineral oil (oily outer phase) containing Span 20 (2%, w/v) 3) evaporation of aqueous solvents under reduced pressure. Details can be found in various publications [208,209]. Chemical cross-linking is an option of this method enzymatic cross-linking can also be performed [210]. Physical cross-linking may take place to a certain extent if chitosan is exposed to high temperature. 

Then when amino groups are cross-linked on the right spots, the enzyme is blocked out from further HP decomposition reactions. Of course, the dialdehydes are not specific either to the enzyme or to the bacteria, but there are enough dialdehyde molecules present to decrease the enzymatic activity to an acceptable level. 

Costes, D., Wehtje, E. and Adlercreutz, P. (2001) Cross-linked crystals of hydroxynitrile lyase as catalyst for the synthesis of optically active cyanohydrins. Journal of Molecular Catalysis B-Enzymatic, 11, 607-612. 

Formaldehyde fixes proteins in tissue by reacting with basic amino acids— such as lysine,5 7—to form methylol adducts. These adducts can form crosslinks through Schiff base formation. Both intra- and intermolecular cross-links are formed,8 which may destroy enzymatic activity and often immunoreactiv-ity. These formaldehyde-induced modifications reduce protein extraction efficiency and may also lead to the misidentification of proteins during proteomic analysis. 

This book gives a comprehensive coverage of the synthesis of polymers and their reactions, structure, and properties. The treatment of the reactions used in the preparation of macromolecules and in their transformation into cross-linked materials is particularly detailed and complete. The book also gives an up-to-date presentation of other important topics, such as enzymatic and protein synthesis, solution properties of macromolecules, polymer in the solid state. The content and presentation of Professor Vollmert s book is more encompassing than most existing treatises, and its numerous figures and tables convey a wealth of data, never, however, at the expense of intellectual clarity or educational value. 

Antigenic determinants masked by formalin-fixation and paraffin-embedding may also be exposed by enzymatic digestion. This can, however, not be used with frozen sections or cells which are not paraffin-embedded. The beneficial effects of protease treatment are presumably related to cleavage of the molecular cross-links by the... 

Figure 19.11 After cleavage of the terminal ends, the collagen molecule begins to assemble into a fibril via enzymatic cross-links. (From Nyman et al., 2005. Copyright 2003, with permission from Elsevier.)...

Berglin M, Delage L, Potin P, Vilter H, Elwing H (2004) Enzymatic cross-linking of a phenolic polymer extracted from the marine algaFucus serratus. Biomacromolecules 5 2376-2383... 

Collagen cross-links. Besides amide bonds between amino acids in the same a chain, bonds between amino acid side chains of different a chains can form "cross-links". These bonds originate from enzymatically-oxidized side chains of lysine and hydroxylysine residues. The oxidized residues react with other lysine and hydroxylysine residues, forming difunctional products. Reactions of such products with oxidized lysine or hydroxylysine yield trifunctional cross-links (Reiser et al., 1992). 

Reiser K, McCormick RJ and Rucker RB (1992) Enzymatic and nonenzymatic cross-linking of collagen and elastin. FASEB J 6, 2439-2449. 

It is noteworthy that several of fhe above-mentioned mediators of discoloration have been found fo inhibif sfrepfococcal proliferation. In addition, collagen cross-linking caused by enzymatic and non-enzymat-ic browning or by tannage with tannins might render dentin less susceptible to proteolytic degradation. 

Further examples of enzymatically degradable drug formulation wrappings are capsule shells made of the polysaccharides chitosan [65,66] or cross-linked dextran [67]. 

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