Protein formation, free

In earlier studies the in vitro transition metal-catalyzed oxidation of proteins and the interaction of proteins with free radicals have been studied. In 1983, Levine [1] showed that the oxidative inactivation of enzymes and the oxidative modification of proteins resulted in the formation of protein carbonyl derivatives. These derivatives easily react with dinitrophenyl-hydrazine (DNPH) to form protein hydrazones, which were used for the detection of protein carbonyl content. Using this method and spin-trapping with PBN, it has been demonstrated [2,3] that protein oxidation and inactivation of glutamine synthetase (a key enzyme in the regulation of amino acid metabolism and the brain L-glutamate and y-aminobutyric acid levels) were sharply enhanced during ischemia- and reperfusion-induced injury in gerbil brain. 

Since, on the acid side, the protein contains free basic groups, and on the alkaline free acidic groups, the assistance to spreading is possibly due to salt formation between the ions in solution and the protein in the film the reason why the least hydrated ions are the most effective may be that they come to the surface most easily, having less affinity for the water than the more hydrated. 

If the antigen or antibody of interest is bound to a soEd phase, such as a cell membrane, or to a synthetic particle (polystyrene or ceEulose), the protein wEl exist in a microenvironment that is dffferent from that of a protein in free solution. The water surrounding the protein is more highly ordered near the surface of the solid phase, and a condition results that is more favorable for van der Waals-London dipole-dipole interaction and coulombic bonding. This situation favors the formation of low- and high-avidity antigen antibody complexes and, hence, can provide lower detection limits for analytical applications. Some studies... 

The reactive site of the cysteinyl residue is the thiol group, which is deprotonated at alkaline pH (pXa around 8.5). The residue under oxidizing conditions (and neutral to alkaline pH) is able to react with a similar residue under formation of a disulfide bond. Many proteins are stabilized by intramolecular disulfide bonds (e.g., insulin, growth hormone, lGF-1), but intermolecular bonds may also result from the reaction under formation of aggregates. In order to avoid unintended disulfide bond formation/cleavage, the redox potential of the solution must be monitored and controlled. In practice, aqueous buffers contain micromolar amounts of dissolved oxygen assuring a redox potential of 200-600 mV, which is sufficient to maintain the intramolecular disulfide bonds. Proteins with free cysteines may... 

Protein and free amino acids found in tobacco leaf contribute significantly through pyrodegradation and pyrosynthesis to the formation of many nitrogenous compounds found in tobacco smoke. The nonvolatility of these compounds either as free acids, proteins, or members of tobacco pigment, for example, porphyrins, make them particularly liable to pyrolytic destruction because they, unlike nicotine and the other plant alkaloids, are not readily volatilized and swept away as the more intense heat of the cigarette coal approaches (3724). 

The steroid hormones act on target cells to regulate gene expression and protein biosynthesis via the formation of steroid-receptor complexes, as outlined in Figure 33.5. The lipophilic steroid hormones are carried in the bloodstream, with the majority of the hormones reversibly bound to serum carrier proteins. The free steroids... 

Another very important factor influencing the reactivity of both reaction partners is pH. Protonisation of the carbonyl group in acidic solutions increases the reactivity of nucleophOic reagents, while protonised amino groups are less reactive as the nitrogen atom does not have a free electron pair (Figure 4.74). Acid base properties of amino acids, peptides and proteins (formation of cations, amphions and anions) are described in Section 2.2.3.1. 

The ultimate goal in studies on the mechanism of protein synthesis is, of course, to follow the fate of a given amino acid step by step, all the way from its free form to its place in a specific protein. Since amino acids, unfortunately, are used not only for protein sjmthesis, but for a multitude of other synthetic reactions as well, the first requirement any potential precursor must fulfill is that its formation and disappearance be kinetically conristent with the rate of protein formation. For this reason it is important to determine the latter as exactly as pos.sible and to study all the possible factors which might influence the apparent rate as determined experimentally from data on amino acid incorporation. The causes for errors... 

---