Shown below is a plot of the solubility of three proteins in increasing ammonium

Question

Shown below is a plot of the solubility of three proteins in increasing ammonium 3., sulfate concentrations. Suggest a procedure to remove protein B, which is the protein of interest, from the other two. (Hint: it takes two steps.) A B C Protein Solubility What is the molecular weight of an unknown prokin if the clution volumes of cytochrome c (MW 13,370), beta-lactoglobulin (MW 37,100), the unknown protein, and hemoglobin (64,500) from a molecular exclusion column are 118, 58, 37, and 24ml, respectively? Assume that all proteins are spherical and fall within the protein ) range of this column.

Explanation / Answer

1. From the plot of protein solubility to ammonium sulphate concentration it can be seen that proteins A, B and C are insoluble at 3M, 5M and 6M of ammonium sulphate respectively. Thus by subjecting the protein mixture to first a 3M ammonium sulphate solution, protein A precipitates out while proteins B and C have high solubilities at that concentration thus separating out protein A from the mixture. Then, the concentration should be increased to 5M at which protein B precipitates out leaving only protein C in the solution thereby separating out protein B also. Finally by evaporating the solution which now contains only C or simply by increasing the ammonium sulphate concentration to 6M, protein C is also obtained in its pure form.

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