THE DETERMINATION OF SERUM TOTAL PROTEIN, ALBUMIN, AND GLOBULIN BY THE BIURET REACTION

Abstract

The biuret reaction for the estimation of protein in urine was first introduced by Riegler (1). Autenrieth (2, 3), Hiller (4), and Fine (5) modified and improved the method. All agreed that the biuret reaction was reliable, the error usually not exceeding 5 per cent in experienced hands. It was also found that equal quantities of albumin and globulin yielded violet colors of practically the same intensity. However, these investigators found it difficult to obtain a satisfactory standard. Biuret was generally abandoned because of impurities and because when treated its color tint differed from that of proteins. Gavrilov and Ginzburg (6) who employed a peptone standard believed that the biuret reaction was suitable only for the estimation of total peptide linkages and not protein. Fine (5) used serum protein preserved in chloroform as a standard which was said to be stable for 6 months. This is quest,ionable, since a deposit often separates from protein solutions on standing. The older methods have been simplified and made more accurate by the elimination of the preliminary precipitation of protein. The procedure has been further shortened by the use of copper su1fat.e and sodium hydroxide in such proportion that precipitate formation is avoided. The need for a standard was eliminated in the method herein described by use of a photoelectric calorimeter.’ Standardization was accomplished by diluting pooled blood serum with 0.85 per cent sodium chloride to give solutions of various