Amino Acid, Peptide, and Protein Volume in Solution

Modern physicochemical biology steadily enriches our knowledge of the functional role of proteins and their elements-amino acids and peptides. These substances are involved in all essential molecular processes occurring in the living cell and perform key regulatory functions at the cellular and organismic levels. Their functional specificity arises from their unique physicochemical properties, specific chemical composition, and the variety of intraand intermolecular interactions of protein residues with each other and with neighboring molecules. As a result, the protein assumes a particular form and volume. Spatial coordinates of the atoms of all macromolecules completely characterize the macromolecule structure. It is difficult to define a portion of space filled by a macromolecule, i.e. the volume. To do so, one must estimate the surface surrounding the macromolecule or the volume of all its atoms and all intramolecular cavities. Nevertheless, there are a number of definitions of macromolecule volume. For example, the concept of hydrodynamic volume is used to characterize a space occupied by the macromolecule together with its impregnating solvent. Or the volume may be defined by measuring the structures observed with the electron microscope, using X-ray small-angle scattering, etc. Of special interest are the macromolecule volume values obtained under conditions approaching natural ones, i.e. without electron beams or X rays, without applying great hydrodynamic fields and hydrostatic pressure, and