Proteins enzymatic cross linking

Enzymatic modification of proteins applicable to foods is reviewed by Whitaker ( ). Described briefly are present uses of proteolytic enzymes for modifying proteins through partial hydrolysis. Major emphasis is placed on those enzymes which bring about aggregation of proteins, cross-link formation, and side chain modification through post-translational changes in the polypeptide chain. 

DNA-protein cross-links are quite abundant DNA lesions in mammalian cells, but per se they are not lethal and can be enzymatically repaired (Chiu et al. 1989, 1990 Oleinick et al. 1986 Chiou et al. 1984). 

The first enzymatically coupled FET is sensitive to penicillin (1). It is composed of two separate FET chips and a silver/silver chloride reference electrode (see Fig. 4). Penicillinase, which produces protons during catalysis, is immobilized on one of the FET chips by utilizing the glutaraldehyde protein cross-linking reaction. The membrane of the reference FET chip contains immobilized bovine serum albumin. 

Several attempts of FruA-catalyzed DHAP additions to simple aliphatic dialdehydes like glyoxal or glutaric dialdehyde have been reported in the literature, but in no case had a product been isolated and characterized [72,85]. Malonic dialdehyde cannot be used because it tends to enolize under protic conditions and engages in polycondensations. Our own extensive studies corroborate that enzymatic assays indicate a consumption of DHAP, but no defined products result according to t.Lc. or NMR analysis. Problematic also is the fact that aliphatic dialdehydes irreversibly destroy enzymatic activity by protein cross-linking [86,87]. 

Labuza, T.P., Warren, R., and Warmbier, H.C. The physical aspects with respect to water and non-enzymatic browning. Nutritional, Biochemical and Chemical Consequences of Protein Cross-linking, M. Friedman, ed.. Plenum Press, New York, pp. 379 -418,1977. 

PL PSi can be produced that is a suitable platform for enzyme immobilization by variations in normal etching techniques with HF. AT-type is preferred due to the higher PL signal. Hydrosilation is a versatile method for surface modification, producing a very stable Si-C bond. The most direct and facile route is photo-initiated. Traditional protein cross-linking chemistty can provide useful functionality for attaching biomolecules to one end of the linker. Significant levels of photoluminescence remain after functionalization. In addition, upon ftmctionalization, the surfaces become resistant to further oxidation. Enzymes, such as GUS and OPAA-2, can be attached and still retain enzymatic activity after attachment. The PSi surface retains PL. Upon product... 

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]. 

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. 

From prior attempts at FruA-catalyzed DHAP additions to glyoxal or glutaric dialdehyde no product had been isolated, probably because the dialdehydes can cause cross-linking of the protein and thereby irreversibly destroy its enzymatic activity. On the other hand, hydroxylated aldehydes were assumed to form stable intramolecular hemiacetals in aqueous solution, which may mask the reactivity of free dialdehydes. Using the branched-chain glutaric dialdehyde 38 as a potential precursor to carbon-linked disaccharide mimetics (Scheme 2.2.5.14), we... 

The weak physical forces that hold together self-assembled nanoparticles are, of course, susceptible to disruption under the influence of thermodynamic and/or mechanical stresses. Hence some workers have investigated ways to reinforce nanoscale structures via covalent bonding. For instance, improved stability of protein nanoparticles, in particular, casein micelles, can be achieved by enzymatic cross-linking with the enzyme transglutaminase, which forms bonds between protein-bound glutamine and lysine residues. By this means native casein micelles can be converted from semi-reversible association colloids into permanent nanogel particles (Huppertz and de Kruif, 2008). 

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