Studies in the Physical Chemistry of the Proteins

Abstract

It has not often been possible to consider the relation between the composition of proteins and their behavior. This has been due, in part, to the complexity of this class of substances; a complexity often as bewildering as the organizations and symmetries of the biological systems which proteins constitute, and always more intricate than the stereochemistry of the simpler organic compounds of which proteins are, in turn, composed. The large molecular weights of the proteins, and the large number of amino acids that combine with each other to produce these vast molecules give abundant evidence of their structural complexity. The failure to correlate the behavior of proteins with their composition has probably depended less upon this complexity, however, than upon incomplete knowledge of the amino acids they contain.Recent advances in the methods of isolating and of estimating amino acids have greatly increased our knowledge of the composition of certain proteins. Thus the composition of casein is now 94.2 per cent 1 known (1). As a result of Dakin's new butyl alcohol method 1 The convention has been followed of referring to the ratio of the weight of the amino acid recovered, to the weight of the protein analyzed as the percentage composition of the protein. The water absorbed by the amino acids during hydrolysis should, of course, be added to the denominator, in order to yield the true percentage composition.

The Dielectric Constant of Solutions of Dipolar Ions.

“…The results on -aminobutyric acid, together with the results on solutions in alcohol-water mixtures, are given in table 4. The results on glycine are essentially the same.…”

“…Similar data are available for the three benzbetaines and glycine betaine, which, as we have pointed out, probably exist wholly in the form of dipolar ions under all conditions. In figure 3 are shown the results of Edsall and Wyman (22) on solutions in ethanol-water and ethanol-benzene mixtures, and in figure 4 fairly constant and there is no considerable difference between the two sets of solvents. This is like the case of the two amino acids studied.…”

“…We have seen from the study of aliphatic amino acids and betaines and of peptides that the dielectric increment increases linearly with the length of the chain between the oppositely charged groups in the molecule. Since it follows from equation 4 that the dielectric increment is approximately proportional to the square of the moment, this implies that in these cases the average value of the square of the distance between the charged groups also increases linearly with this length. This agrees with statistical deductions.…”

Aqueous Zein Dispersions

“…A patent issued to Osborne and Cornelison (8) was based upon the extraction of zein from crude corn gluten by adding to a water suspension of this gluten "enough caustic soda or caustic potash to impart to the mixture a decided alkaline reaction with phenolphthalein." Cohn, Berggren, and Hendry (6) found that zein will not readily dissolve in aqueous ammonia, and that a pH of 10 or higher must be reached before solution occurs in alkali. Smith,Max,and Handler (9), during studies on the dispersion of proteins in formaldehyde, found that maximum dispersion of zein in alkali was obtained at a pH of approximately 12.6, and that the addition of formaldehyde shifted the point of maximum dispersion to a pH of approximately 10.7.…”