The Molecular Structure of Amino Acids : Determination by X-Ray Diffraction Analysis

The last decade has seen great progress in the study''of the structure and functions of living organisms at the molecular level; molecular biology has become a new branch of science [1-16]. One of the major problems of molecular biology concerns the structure of proteins. Some information about protein structure is provided by the electron microscope, by the ultracentrifuge, and by small-angle x-ray scattering; the last gives the fullest information about the atomic structure of protein molecules, but x-ray study of biological objects represents a difficult and laborious task. In this way the struc­ tures of three proteins have been established: hemoglobin, myoglobin [2, 8J, and lysozyme [10]; work has begun on ribonuclease, insulin, chymo­ trypSin, carboxypeptidase, and so on [14-16]. A knowledge of the structures of amino acids and peptides is of con­ siderable value in elucidating the structure and functions of proteins. Near­ ly all proteins consist largely of 22 principal amino acids, which are linked together in polypeptide chains. The peptide link always arises between an a-amino group and the carboxyl group in the next amino acid residue, so all polypeptide chains have the same backbone, to which are attached dif­ ferent radicals R (Fig. 1).