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    Determining the subunit composition of a protein from data

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    You isolate a new protein. Column chromatography, in Tris-HCl buffer pH 7.4, demonstrates that this protein has a molecular weight of 110,000 D. Chromatography in the presence of 6 M guanidine hydrochloride demonstrates two peaks with masses of approximately 13,000 and approximately 26,000 D. The peak at approximately 26,000 D contains 80.3%, by mass, of the protein. The protein from this peak, when analyzed using isoelectric focusing column chromatography demonstrates that this peak contains two different proteins, each being 50% of the mass of this peak and both with acidic pIâ??s. These two 26,000 D proteins are separately treated with a^-mercaptoethanol and analyzed by column chromatography in the presence of 6 M guanidine hydrochloride. This demonstrates equal amounts of three peptides with molecular weight of 10,000 D, 9,000 D, and 7,500 D for one protein and 17,500 and 9,000 for the other protein. From these data, determine what the composition of this new protein is.

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    Solution Preview

    This should be a multi-subunit protein with the following composition:

    2 of the 13 kDa subunits (since the first two peaks showed an approximate 80% to 20%, the 20% being the 13000 D weight. 80% was the 26 kDa peak).

    The 26 kDa protein is further broken up ...

    Solution Summary

    In this solution we explore how to elucidate the number and types of subunits of a multi-unit protein from biochemical data. A detailed approach to the problem is provided in the solution.