An Assessment of Some of the Methods Available for the Determination of Molecular Weights of Proteins as Applied to Aspartate Aminotransferase from Pig Heart

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Abstract
The isopotential specific volume of cytoplasmic aspartate aminotransferase [EC 2.6.1.1] from pig heart was 0.763 ml g-1; the value of the apparent specific volume obtained by summation of contributions from each type of amino acid in the protein is 0.735 ml g-1. Use of the experimentally determined isopotential specific volume largely abolishes the discrepancy between a previously reported value of the MW of the native (dimeric) enzyme and that of the enzyme subunit obtained from its primary structure (46,300). A new non-empirical method based on quantitative N-terminal analysis involving radioisotope dilution is described for the determination of subunit molecular weight of proteins. The method is capable of considerable accuracy and sensitivity. Some of the methods available for the determination of molecular weights and subunit compositions of proteins are discussed.