Gerson Kegeles

The molecular weights of ribonuclease and bovine plasma albumin

Abstract With the methodology outlined, it now appears possible, by use of the Archibald procedure, to obtain a reliable value for the molecular weight of a protein within an hour of sedimentation in the ultracentrifuge. The ultracentrifugal data so obtained need be supplemented only by a measurement of partial specific volume. As previously demonstrated, the same method also holds through the whole molecular weight range down to 504, and recent data of Wade (25) obtained in this laboratory for glycyl- l -leucine indicate equal precision for a molecular weight of only 188.

Macromolecular degradation products of bovine plasma albumin

Abstract With the aid of a recording interferometer, gradient elution chromatograms from diethylaminoethylcellulose were obtained for chymotrypsin, for bovine plasma albumin, and for dialyzed chymotrypsin- and hydrochloric acid-hydrolyzates of bovine plasma albumin. In the case of the hydrolyzates by chymotrypsin, fractions collected at 1.2-ml. intervals were subjected to molecular-weight determinations with the Archibald technique. The hydrolyzates were also examined electrophoretically. From the combined data of the chromatographic recorder and the ultracentrifuge it was possible to construct molecular-weight-distribution curves for the dialyzed hydrolyzates. Hydrolysis of bovine plasma albumin by chymotrypsin for 24 hr. at 37 °C. was found to lead to macromolecular products containing about 10% of a peptide material of molecular weight 19,000, and small amounts of materials with molecular weights higher than that of albumin, in addition to a preponderant amount of material having the molecular weight of albumin. Electrophoresis of this hydrolyzate also demonstrated the presence of two major components.

THE EFFECTS OF PRESSURE IN HIGH‐SPEED ULTRACENTRIFUGATION OF CHEMICALLY REACTING SYSTEMS

A system of the type A + B & AB has been investigated by preassigning the required starting values of concentrations and such physical parameters as rotor speed, length and position of liquid column, density of solution, partial specific volumes and molecular weights. Predictions were then made of the distribution of each species a t equilibrium, and from this information, observable values of total concentration and concentration gradient everywhere in the column were predicted, as well as derivable quantities such as local values of the weight average molecular weight and the equilibrium constant, assuming thermodynamic ideality. By comparing the distribution with one calculated in the absence of pressure effects (zero volume change of reaction), we might estimate how accurately one needs to measure concentration gradient or concentration across the column in order to arrive at molecular weights of desired accuracy, or meaningful values of nonideality coefficients in the presence of pressure effects. The starting point in the calculation might be taken as the ideal solution law sedimentation equilibrium equations for the species A, B, and AB, which still hold even when a chemical reaction imposes restrictions on the overall distribution of material:

Formation constants of weak complexes. Determination for HgClBr by countercurrent distribution

Abstract The relationships drawn by Bethune and Kegeles to allow predictions of the countercurrent distribution patterns of chemically reacting systems from assigned values of equilibrium constants have been usefully inverted for a model system involving a weak complex. From experimental countercurrent distribution patterns for the system mercuric chloride, mercuric bromide, mercuric chlorobromide, accurate values for the formation constant for the chlorobromide have been obtained in water and benzene. The formation constant is in agreement with the results of Delwaulle and Francois from Raman spectroscopy. It is hoped that this example may stimulate the application of the countercurrent distribution method to the study of weak complexes of biochemical origin.