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Handbook of Size Exclusion Chromatography and Related ...

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Figure 4 Chromatograms <strong>of</strong> BSA <strong>and</strong> Protein X obtained under identical SEC<br />

conditions. Owing to interaction with the stationary phase, Protein X eluted much later than<br />

the BSA monomer. MALS detection determined a molecular weight <strong>of</strong> 57kD for Protein X,<br />

as expected from its sequence.<br />

conformation <strong>of</strong> glycosylated or pegylated proteins are much more extended than<br />

the unmodified proteins but more dense than the free polysaccharides <strong>and</strong><br />

polyethylene glycol. Therefore, molecular weight <strong>of</strong> the modified proteins<br />

measured by traditional column calibration with either protein or polymer<br />

st<strong>and</strong>ards will lead to significant errors (78). Wen <strong>and</strong> co-workers demonstrate the<br />

use <strong>of</strong> combining MALS, UV, <strong>and</strong> RI detectors to measure both the molecular<br />

weight <strong>of</strong> each component in the complex <strong>and</strong> the degree <strong>of</strong> modification (73).<br />

6 PREPARATIVE PROTEIN SEC<br />

The inherent effectiveness <strong>of</strong> SEC for large-scale protein purification is based on<br />

the equilibrium nature <strong>of</strong> the method, which results in high yields because little<br />

solute is denatured, <strong>and</strong> in predictability <strong>of</strong> elution once column parameters are<br />

known.<br />

6.1 Applications<br />

The first industrial application <strong>of</strong> SEC for protein solutions was for desalting dairy<br />

products (79). Large columns (2500L) were used to separate proteins in whey or<br />

skim milk from low molecular weight sugars <strong>and</strong> salts. SEC is also used in the<br />

“de-ethanolization” <strong>of</strong> human serum albumin (HSA) (80) produced by the Cohn<br />

cold ethanol procedure. The purification <strong>of</strong> insulin was the first successful<br />

© 2004 by Marcel Dekker, Inc.

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