Chemical, Clinical, and Immunological Studies on the Products of Human Plasma Fractionation. Iii. Amino Acid Composition of Plasma Proteins 1

The determination of the proportions of the amino acids that are liberated when proteins are subjected to complete hydrolysis provides information of value from many points of view. Amino acids are the fundamental units from which the protein molecule is constructed since the basic pattern of the structure depends upon the combination of the a-carboxyl group of one amino acid with the a-amino group of its neigh-bor to form peptide linkages. Accordingly, the conclusion may be drawn that the accessory polar groups of the basic and dicarboxylic amino acids commonly found in proteins are for the most part either free or are available for chemical combinations of various degrees of stability. Such combinations may occur between two polar groups located sufficiently near together within the same molecule, or they may give rise to interaction between separate protein molecules, or between the protein molecule and the mole-cules or ions of substances likewise present in the solution, or between the protein molecule and the molecules or ions of the solvent itself. The physical chemical analyses of the human plasma fractions which are set forth in Paper I of this series (1) treat them as more or less elon-gated ellipsoids. The surface of these molecules may be considered as containing numerous dis-crete points at which a wide variety of chemical I The present analytical studies of plasma proteins have been carred out under contract, recommended by the Committee on Medical Research, between the Office of Scientific Research and Development and Columbia Uni-versity. The preparations examined were, with one or two exceptions, made from blood collected by the American