Sensitization covalent bonds with proteins

As a rule, simple chemicals which are potent sensitizers are also highly reactive and can readily be shown to form conjugates with proteins in vivo. Those chemicals unable to form covalent bonds with proteins in vitro show no or only a very low incidence of sensitization. The extent to which a simple chemical is reversibly bound to serum proteins such as albumin has no apparent influence on its ability to sensitize. In several instances, the antibodies formed on sensitization with a simple chemical in vivo are specific not for the original compound injected, but for the modified haptenic structure formed on covalent binding to a protein carrier. 

H is particularly important in NMR experiments because of its high sensitivity and natural abundance. For macromolecules, 1H NMR spectra can become quite complicated. Even a small protein has hundreds of 1H atoms, typically resulting in a one-dimensional NMR spectrum too complex for analysis. Structural analysis of proteins became possible with the advent of two-dimensional NMR techniques (Fig. 3). These methods allow measurement of distance-dependent coupling of nuclear spins in nearby atoms through space (the nuclear Overhauser effect (NOE), in a method dubbed NOESY) or the coupling of nuclear spins in atoms connected by covalent bonds (total correlation spectroscopy, or TOCSY). 

Covalent bonds between oxidized phenolics and proteins were shown to be more likely to form at high pH since phenolics are more readily oxidized at high pH. This was particularly true with basic proteins and less so with acidic proteins.124163164 Because precipitation of phlorotannin-protein complexes was independent of temperature, hydrophobic forces were not considered likely to be important in their formation.124 164 These studies suggest that, although phlorotannin structure is important, at least part of the variation in sensitivity to dietary tannins is due to variation in herbivore gut chemistry. 

On the contrary, the nutritional value of oxidized lipid-protein interaction products is substantially lower than that of the original lipoproteins. The main reason is the lower digestibility most covalent bonds formed in the interactions are not attacked by proteases under the conditions of digestion. The 6-amino group of bound lysine is particularly sensitive to interactions with carbonylic oxidation products (Janitz et al., 1990), and the resulting imine bonds substantially reduce the lysine availability. Lysine losses correlate with the increase in fluorescence. Other amino acids, such as tyrosine, tryptophan, and methionine, are also partially converted into unavailable products. Interaction products may be allergenic even when allergenic proteins have reacted (Doke et al., 1989). 

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