Biomolecular absorption of ultrasound: II. Molecular structure.

Measurements of absorption coefficients in several globular and linear proteins yield no correlations of absorption with alpha-helix content or with the number of polypeptide chains in the protein. Removal of all but the primary structure with denaturing agents that convert proteins to random chains causes only small changes in the absorption of globular proteins. Complete denaturing of linear muscle proteins results in large reductions in absorption. Therefore, it is concluded that absorption in globular proteins is insensitive to structural characteristics while in linear proteins it is dependent upon the amount of alpha-helix content. An alternative explanation of the results is that alpha-helix contributes to absorption in both globular and linear proteins but tertiary structure in globular proteins reduces absorption because of inhibited solvent interactions.