Application of Theory to Protein Fractionation

It has been said that to obtain good separation of proteins by salt fractionation it is advantageous to use a high concentration of protein. The efficiency of separation is determined by the width of the p6aks in the distribution curve and their separation. The theory indicates that the width of a given peak is independent of the protein concentration (see footnote 2). 

The effect of the concentration of any protein on the position of its peak is determined by the value of Ka for that protein. Therefore in a mixture of proteins with different Ka values the relative positions of the various peaks will vary with the concentration of the mixture, as pointed out by Falconer et al. (1953). The effect of this on the efficiency of the fractionation is unpredictable unless the values of Ka are known. The effect of diluting a mixture may be to separate two peaks that were previously overlapping, as in the case considered in Fig. 8c to ji on the other hand dilution may bring together peaks that were previously well separated. Protein concentration is clearly a variable that should be taken into account in finding the best conditions for the isolation of any particular protein, and it may be worth 

Excessive dilution, however, should be avoided for three reasons. Since dilution shifts all the peaks to higher concentrations, an increasing propor- 

The theory can be used to throw light on the size of step which should be chosen in isolating a protein from a mixture. It is not infrequent to read of the use of very wide fraction limits in enzyme preparations, e.g., from 

If the protein is contaminated by overlap of the tail of a preceding peak, one might suppose at first sight that the purest fractions would occur 

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