Ovalbumin, denaturation

Proteins are prone to denaturation at both high and low temperatures. Although cold denaturation is frequently mistaken for freezing denaturation, it is known to occur in the absence of freeze concentration. For example, as early as 1930 it was reported that the rate of ovalbumin denaturation by urea is higher at 0°C than at 23°C [50]. Privalov provides a comprehensive review of the subject [51]. 

FIGURE 8.12 Effect of pore diameter on SEC of standards (nondenaturin > mobile phase). Nondenaturing" refers to the effect on the stationary phase. Most iarge proteins were in fact denatured by this mobile phase (which was optimized for use with peptides, not proteins). Accordingly, it was necessary to use polyacrylamide to demonstrate the approximate range and position of Vo under these conditions. The polyacryiamide standards both eiuted at V with the 300-A coiumn (not shown). Columns and flow rate Same as in Fig. 8.11. Mobile phase Same as in Fig. 8.1. Sample key (B) Ovalbumin (43,000 Da) 0) polyacrylamide (1,000,000 Da) (K) polyacrylamide (400,000 IDa) (L) low molecular weight impurity in the polyacrylamide standards. Other samples as in Fig. 8.11. 

Koseki, T., Kitabatake, N., Doi, E. (1989). Irreversible thermal denaturation and formation of linear aggregates of ovalbumin. Food Hydrocolloids, 3, 123-134. 

Proteins of egg white denature more rapidly than those of whey protein concentrate (13, 34). However, isolated p-lactoglobulin from the whey concentrate was more susceptible to surface denaturation than egg white ovalbumin. These data suggest that whey contains substances that protect the proteins from surface denaturation and may account for the lower stability of whey protein concentrate foams than those of egg white protein. A balance between the disaggregation effect of select pH values and the tendency toward greater aggregation of proteins at higher heating temperatures were correlated closely with maximum foam stability (13, 15). 

Thermal treatment of proteins present in processed foods may have implications beyond food safety to the functionality of these proteins. For this purpose, specific antibodies raised against native and denatured proteins which could distinguish the two forms would enable one by immunoassay to determine the extent of protein denaturation in the product and its associated implication in safety and functionality of the finished food. Paraf (87) discusses this aspect in his review on monoclonal antibodies in the analysis of food proteins. The ability of IA s to distinguish native versus heat-denatured ovalbumin dependent on the assay protocol used. One can foresee this... 

R. Nakamura, Studies on the foaming property of the chicken egg white, Part VII, On the foaminess of the denatured ovalbumin, Agr. Biol. Chem. 28 (1964) 403-407. 

Wu, H. and S. M. Ling Denaturation of proteins. V. Factors controlling coagulation of proteins by shaking. Separation of ovalbumin from conalbumin. Chinese J. Physiol. I, 407 (1927). 

From electric birefringence measurements it was concluded that the proteins are ordered head-to-tail within the fibril, in a helical configuration (Rogers et al. 2005). The fact that one needs a minimal temperature in order to induce fibrillisation is directly related to the fact that at a certain elevated temperature the protein will partially unfold. Since we have also observed the formation of fibrils at 4°C, after having applied this (partial) denaturation step, the elevated temperature is not essential during assembly. However, at the lower temperature, the assembly was found to be much slower, indicating that temperature affects the kinetics of the assembly process. The relation between the fibrillar type of assembly and the partially unfolded state also has been found for other proteins (e.g., ovalbumin, hen egg white... 

With several other proteins, such as bovine serum albiunin (Tanford and Roberts, 1952), lysozyme (Tanford and Wagner, 1954), and/3-lacto-globulin (Tanford and Swanson, 1957), pK shifts of the phenolic OH groups of tyrosine residues are observed, but these are of a qualitatively different nature. Thus, the tyrosines of any one of these proteins cannot be readily differentiated into a normal and an abnormal variety, since the spectrophotometric titration data for these proteins are reversible and fall on single smooth curves, in contrast to the situation with RNase. On the other hand, the tyrosine residues of ovalbumin show comparable behavior to the three abnormal tyrosine groups of RNase (Crammer and Neuberger, 1943). About 2 of the total of 9 tyrosine residues appear to titrate normally, but the remainder are not titrated up to pH 12. At pH 13, these anomalous tyrosines become titratable, and this is accompanied by the irreversible denaturation of the ovalbumin molecule. 

Fig. 7. The temperature (Tj) and enthalpy (Hi) of denaturation of ovalbumin as functions of the water content. From Fujita and Noda (1981b).

On the other hand, the dispersions obtained by Yang and Doty (1957) for poly-y-benzyl-L-glutamate in a mixture of /3-forms and coil forms did not obey the simple Drude equation, and Imahori s analysis of these data yielded positive Moffitt slopes and intercepts after corrections had been made for the intrinsic residue contribution (Imahori, 1960). Imahori has moreover found that denatured bovine serum albumin and ovalbumin in solution display positive ba and corrected ao values in sharp contrast to the negative slopes characteristic of the native proteins and has in addition been able to correlate the positive slopes with the /3-form in the protein precipitates by infrared spectra. Wada et al. (1961) have recently carried forward this suggestion that the (8-conformation displays complex disper-... 

This is a very useful rule. It is only a rough rule—the 10 factor for most reactions is close to 2, but occasionally it is as small as 1.5 or as large as 4. Reactions of very large molecules, such as proteins, may have even larger temperature factors the rate of denaturation of ovalbumin (the process which occurs when an egg is boiled) increases about fiftyfold for a 10 rise id temperature. 

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