Protein concentrates radicals

Radiation targeting involved exposing proteins to (OH/e g) or exclusively OH radical attack and then correlating activity loss with radiation dose. This correlation, using a set of empirically designed relationships, allowed a determination of protein size. It was, however, dependent upon a number of parameters such as temperature and protein concentration. Recent research carried out by Houee-Levin and co-workers as well as other groups have shown this technique to be dependent upon the judicious choice of protein and the empirical correlations fail in a wide number of systems. 

Figure 2. Time-resolved absorption changes induced by reaction of pulse radiolytically produced C02 radicals with P. aeruginosa azurin. (a) Reduction of Cu(II) followed at 625 nm. (b). Formation and decay of the di sulfide radical anion measured at 410 nm. Protein concentration is 1 OpAf, where T = 298 K pH 7.0 0.1M formate 10 mM phosphate N2O saturated pulse width 0.4 ps optical path 12.3 cm. Time is in seconds the left panel shows the faster phase, while the right one shows the reaction taking place at the slower phase. The lower panels show the residuals of the calculated fits to the data.

Later pulse radiolysis experiments demonstrated that, following a bimole-cular reduction of TlCu by the reducing radicals, TlCu reoxidation at 605 nm and concomitant T3Cu reduction at 330 nm could be monitored independently and directly (48) (cf. Fig. 8). The rate of the latter reactions was independent of protein concentration, consistent with being a unimolecular process. An unprecedented feamre in AO was that at least two parallel phases of intramolecular ET were resolved. For the first phase, a rate constant of 200 s was determined... 

Studies on Mb(Fe = O) in our laboratoiy were carried out by pulse radiolysis. This avoided problems associated with photoinduced Fe ==0 heme autoreduction as was observed in the flash photolysis studies on CCP. Furthermore, low concentrations (0.5-2 [jlM) of a5Ru(His48)HHMb(Fe =0) were sufficient to react with the long-lived CO2 radical and for optical detection of heme reduction in the Soret region (Ae 100 mM cm ) (26, 49). The use of low protein concentrations promotes intramolecular Ru heme ET reactions over intermolecular ET reactions (equations 8 and 9). Further studies on Fe =0 heme reactivity will be preferentially carried out by pulse radiolysis because of the advantages enumerated here. 

In addition to the products of lipid oxidation, methanethiol and dimethyl trisulfide were shown to contribute to the complex odor characteristic of soy protein products such as SPI and soy protein concentrates (Boatright Lei, 2000 Lei Boatright, 2001) and soymilk (Lozano et al., 2007) at concentrations comparable to hexanal. Since the threshold in water for methanethiol was reported at 0.02 ppb compared to hexanal at 4.5 ppb (MacLeod C Ames, 1988), these sulfur compounds are intense flavor notes in soy protein products. Lei and Boatright (2007) provided evidence that methanethiol is generated in aqueous slurries of SPI or defatted soy flake from methionine by a free radical mechanism involving manganese, sulfite, and... 

Phytic acid and camosine (histidine-containing dipeptide), obtained from cereal and meat by-products, are effective inhibitors of hpid oxidation by several mechanisms, including metal inactivation and free radical quenching. Uric acid obtained from the decomposition of adenosine triphosphate in muscle also inhibits lipid oxidation by the same mechanisms. However, the importance of uric acid as an endogenous antioxidant in muscle foods is not clear. Various protein concentrates from soybeans, cottonseed and peanuts inhibit hpid oxidation in muscle foods. In addition to their iron binding activity, these crade extracts contain complex polyphenolic flavonoids that have potent antioxidant activity. 

Exposure of human red blood cells from healthy adult volunteers of either sex to high concentration of HOCl and HOBr (>40 nmol/10 cells) resulted in rapid cell lysis and the detection of an additional nitrogen-centred, protein-derived radical adduct (Hawkins et al. 2001). HOBr induced red blood cell lysis at approximately 10-fold lower concentration than HOCl, whereas with monocyte (HTPl) and macrophage (J774) cells HOCl and HOBr induced lysis at similar concentrations. Erythrocytes exposed to nonlytic doses of HOCl generated novel nitrogen-centred radicals the formation of which is GSH dependent. 

The biochemical basis for the toxicity of mercury and mercury compounds results from its ability to form covalent bonds readily with sulfur. Prior to reaction with sulfur, however, the mercury must be metabolized to the divalent cation. When the sulfur is in the form of a sulfhydryl (— SH) group, divalent mercury replaces the hydrogen atom to form mercaptides, X—Hg— SR and Hg(SR)2, where X is an electronegative radical and R is protein (36). Sulfhydryl compounds are called mercaptans because of their ability to capture mercury. Even in low concentrations divalent mercury is capable of inactivating sulfhydryl enzymes and thus causes interference with cellular metaboHsm and function (31—34). Mercury also combines with other ligands of physiological importance such as phosphoryl, carboxyl, amide, and amine groups. It is unclear whether these latter interactions contribute to its toxicity (31,36). 

S-Thiolation of proteins may occur by two main processes as shown in Fig. 4.14. The first relies on an increase in GSSG levels while the second method depends on free radical production and the GSH concentration (Miller et al., 1990). Therefore, it is clear that a significant increase in tissue GSSG levels is not an absolute prerequisite for S-thiolation to occur. 

---