Universal size-independent quantities for the conformational characterization of rigid and flexible macromolecules

Abstract

Solution properties of macromolecules can be combined to form dimensionless quantities that are universal in the sense of depending on the shape or conformation of the macromolecular solute, being independent of its size. A number of such quantities have been formulated at different times by different authors, and as a consequence they differ widely from one to another, not only in their notation and the order of magnitude of their values, but also in the way in which the primary solution properties enter in them. In this work we propose a new set of universal size-independent quantities in a systematic and consistent way. First, solution properties are expressed in the form of radii of an equivalent sphere. Then the equivalent radii are combined to give ratios of radii. We propose the use of the ratios of radii as indicators of macromolecular conformation. Examples of their values are given for three macromolecular structures: (1) ellipsoids, with application to globular proteins, (2) oligomeric arrays of subunits, with seed globulins as examples and (3) flexible-chain macromolecules, illustrated by polystyrene in two solvents.