The Basic Amino Acids of Serum Proteins

The importance of a classification of proteins based on amino acid composition has been previously pointed out (1,2). A measure of success has been achieved only with the keratinoid tissues and the protamines (3). The protamines, moreover, seem to form a special class of proteins. This leaves the keratins as the only true proteins which have been classified on a purely chemical basis. Rlock and Vickery (2) showed that keratins of widely differing origins yielded on acid hydrolysis amounts of histidine, lysine, and arginine in the molecular ratios of approximately 1: 4 : 12 (2, 4). In every case the material analyzed comprised the entire protein portion of the tissue. In other words, the keratinoid tissues contained histidine, lysine, and arginine in a remarkably constant proportion although the actual percentage of these bases present in the tissue varied as much as 1000 per cent. On the other hand, it has been indicated that the albumins and globulins obtained from cattle serum by precipitation with various neutral salts are not of constant basic amino acid composition but are simply artificial products produced by the reagents employed in their preparation. However, in every case, the more soluble protein fractions (albumins) obtained by this technique yielded more lysine than the less soluble fractions (globulins). These studies indicated that if the albumin-globulin determinations as carried out in the clinic were real estimations of the amounts of albumin and globulin present in a serum, then two sera with