Molecular composition isoelectric focusing

These two polypeptides have been shown to have identical amino acid composition (Table 9) but to differ from each other in sialic acid content. Da and D4 have 1 and 2 moles of sialic acid per mole of protein, respectively (A5, A6, B9, BIO, E5). A third form without sialic acid has been isolated by preparative isoelectric focusing (A5). Both D3 and D4 have the same NHa-terminal (serine) and COOH-terminal (alanine) amino acid residue and a molecular weight of about 10,000. The complete amino acid sequence has recently been announced (B6) and is reported in Fig. 7. These studies show that the polysaccharide having sialic acid as its terminal sugar, is linked to threonine 74 of the polypeptide chain. 

Polyacrylamide gel electrophoresis is one of the most commonly used electrophoretic methods. Analytical uses of this technique center around protein characterization, for example, purity, size, or molecular weight, and composition of a protein. Polyacrylamide gels can be used in both reduced and nonrcduced systems as well as in combination with discontinuous and isoelectric focusing (ief) systems. 

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