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A sedimentation equilibrium study of ovomucin Miller, Steven Michael


Sedimentation equilibrium ultracentrifugation was used to detect heterogeneous protein-protein assocations in interacting mixtures of lysozyme and ovomucin and to determine the change in molecular weight of ovomucin during egg white thinning. Molecular weight distribution (MWD) patterns calculated from sedimentation equilibrium data using multiple regression analysis revealed the presence of a temperature-sensitive interaction at pH 6.9 between lysozyme and ovomucin at ionic strengths of 0.13 and below. The extent of interaction differed depending on the method of preparation of ovomucin. The interaction of lysozyme was stronger with β-ovomucin than with α-ovomucin and removal of sialic acid residues from β-ovomucin did not decrease this interaction but acetylation of lysozyme did. Self-association of α-ovomucin at low ionic strength was also observed. The apparent molecular weight of native ovomucin isolated from blended fresh egg white by gel filtration on Sepharose 4B was 5.64 x 10 at pH 6.95 and ionic strength 0.13. Detailed ultracentrifugal analysis indicated a remarkable dependence of molecular weight on protein concentration. The apparent molecular weight, amino acid and carbohydrate compositions of native ovomucin were similar to those of ovomucin isolated from egg white that had been stored for 166 h at 30°C. The molecular weights of ovomucin, isolated by gel filtration on Sepharose 4B of fresh egg white reduced with 0.02% 2-mercaptoethanol, were 309,500 and 726,200. It is thus considered that disulfide cleavage of ovomucin does not occur during natural thinning. The relation of the results obtained in the present study of ovomucin to the mechanism of egg white thinning was also discussed.

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