From the point of view of organic chemistry, the establishment of the empirical formula (cf. Mulder,l in 1838) of proteins, in terms of constituent amino acids, is fundamental to an understanding of their constitution and to the development of theories of protein structure.An apparently complete analysis of a simple, crystalline, homogeneous protein of small molecular weight (42,0OO), P-lactoglobulin, has recently been presented.2 Although, doubtless, there will be future improvements in detail, this paper is the first to describe a complete analysis of a single preparation of a protein by the same group of workers.Many of the data were obtained in the course of the development and standardization of methods for application to plasma proteins. This represents part of the comprehensive program of the Plasma Fractionation Laboratory, at Harvard University, under the direction of Dr. Edwin J. Cohn. A considerable part of the work presented here was carried out under contract, recommended by the Committee on Medical Research, between the Office of Scientific Research and Development and Columbia University.Data on P-lactoglobulin, 'bovine serum albumin, human y-globulin, and crystalline insulin will be given. Alanine is the only amino acid which has not been determined in these proteins (except in P-lactoglobulin) . All the values given in these tables are our own results.*
METHODS OF ANALYSISOur methods are summarized in TABLE 1. Some of these methods have been reported in detail; others, in outline; and some are, as yet, unpublished. They cover a wide range of chemical manipulations, from ultraviolet absorption, micro-diffusion, micro-titration, and photometry to micro bioassays, with Neurospora mutants and different strains of Lactobaccilli, and enzymatic methods with the specific decarboxylase of Bacterium cadaveris. The development of the bioassays was possible as the re-* In the development of the work, Dr. , from 'the Department of ioology, have taken part for the past few years and much credit is due to them.
