Disulfide ovomucoid

Kato, Y., Oozawa, E., Matsuda, T. 2001. Decrease in antigenic and allergenic potentials of ovomucoid by heating in the presence of wheat flour Dependence on wheat variety and intermolecular disulfide bridges. J Agric Food Chem 49 3661-3665. 

Figure 17. The effect of disulfide bond modification of turkey ovomucoid by alkali on inhibitory activity against trypsin (T), a-chymotrypsin, (C), and subtilisin (S). Turkey ovomucoid (O.lOmM) was treated with alkali (lOOmM NaOH) at 23°C. Sulfhydryl content (moles per mole of protein)...

B Elimination has been used to show differences among the disulfide bonds in various proteins including the ovomucoids (54). The e-elimination reaction has also been used to replace the hydroxyl group of the essential serine residue of subtilisin with a sulfhydryl group (55). The thiolsubtilisin had a small fraction of the activity of subtilisin but it has been quite useful in mechanistic studies of the serine and sulfhydryl proteases. 

Figure 8. Reformation of disulfides and inhibitory activities on reoxidation of reduced turkey ovomucoid, a dual inhibitor of bovine trypsin, and a-chy-motrynsin with nonoverlapping sites. The disulfides of turkey ovomucoid were reduced with mercapto-ethanol and the product purified. Reoxidation was made with protein concentrations of 60 fxg/ml in 0.006M. Tris buffer at pH 8.2 at room temperature. (Turkey ovomucoid contains eight disulfides, all of which were reduced to 16 sulfhydryls in this experiment. Of these 14 were found at the first sampling and five at the time the experiment was discontinued.) A9 Trypsin inhibition O, a-chymotrypsin inhibition , sulfhydryls per mole (33).

Chemical modification by disulfide bond cleavage can markedly alter thermal stabilities or other properties of the inhibitors, since disulfide crosslinks help maintain the active conformations of many proteinase inhibitors (Laskowski and Sealock, 1971 Tschesche, 1974 Weder, 1981). Loss of thermal stability resulting from reductive alkylation of disulfide bonds has been observed for BPTI by H-NMR (WQthrich et al., 1980), for proteinase inhibitor I from potato by immunological assay (Plunkett and Ryan, 1980), and for STI, LBI, and chicken ovomucoid by DSC (Friedman et al., 1982c). 

Ovomucoid and ovomucin are the proteins responsible for the viscosity and gel-like consistency of egg white. Ovomucoid (28 kDa, p7=4.4-4.6) is composed of three components which differ in carbohydrate composition on the JV-terminus of the molecule. Ovomucoid inhibits trypsin and other proteolytic enzymes and is a strong allergen. The stability to thermal denaturation (in an acidic medium) is associated with nine disulfide bonds in the molecule. 

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