|Budget Amount *help
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1990 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1989 : ¥1,500,000 (Direct Cost : ¥1,500,000)
To elucidate the fluctuation-structure-function relationships of food proteins, the adiabatic compressibility, beta, of various egg and milk proteins was determined by means of sound velocity and density measurements in aqueous solutions. All the protein showed positive beta values, indicating the large internal flexibility characteristic of the protein molecules. On the basis of statistical analyses of beta, the flexibility-structureーfunction relationship was discussed in terms of the internal cavity and hydration, focusing on the hydrophobicity of proteins. It was found that beta increases with increasing partial specific volume and hydrophobicity of proteins. The helix element also seemed to be a dynamic domein to increase beta. Four amino acid residues (Leu, Glu, Phe, and His) greatly increased beta, and another four (Asn, Gly, Ser, and Thr) decreased it. Some empirical equations were derived for the estimation of the beta values of unknown proteins on the basis of their amino acid compositions. The volume fluctuations of proteins revealed by the compressibility data were in the range of 30-200 ml/mol, which corresponded to about 0.3 % of the total protein volume. Most proteases and protease inhibitors were less compressible compared with nutrient (storage) proteins such as egg and milk proteins while an extreemely high flexibility was observed for the transport proteins. Protease susceptibility, foaming capacity, and free energy of unfolding of proteins were positively correlated to beta. The conformational fluctuation seemed to enhance the thermal stability of proteins. These results indicate that the flexibility of the structure plays an essential role in the conformational stability and functional properties of food proteins.