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Handbook of Size Exclusion Chromatography and Related ...

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Table 5 Molecular Weight Distribution by SEC-LS: Biopolymers: Selected Applications<br />

Macromolecule References<br />

Proteins 97,184–198<br />

Membrane proteins 198–204<br />

Enzymes 205,206<br />

Nucleic acids 207<br />

for studying protein association. In using an on-line light-scattering detector for<br />

SEC <strong>of</strong> proteins, it seems logical to use assigned dn=dc values for individual<br />

proteins, determined <strong>of</strong>f line using purified samples. In many cases, however,<br />

purified st<strong>and</strong>ard proteins are not available, there is limited sample availability,<br />

or the identity <strong>of</strong> proteins in asample is not known. Because <strong>of</strong> the uncertainty<br />

in dn=dc values, many investigators have used both adifferential refractometer<br />

<strong>and</strong> a UV spectrophotometer, in series with a light-scattering detector, to<br />

determine dn=dc values <strong>of</strong> eluting species. For example, Maezawa <strong>and</strong> Takagi<br />

(198) used this approach to determine the molecular weights <strong>of</strong> glycoproteins.<br />

Alight-scattering-UV-DRI (differential refractive index) detection system has<br />

also been used for determining molecular weights <strong>of</strong> ATPases (192,206) <strong>and</strong><br />

membrane proteins (208). Recently, Krull <strong>and</strong> co-workers (185,209)<br />

investigated the advantages <strong>of</strong> using the LS-UV-DRI approach for protein<br />

characterization <strong>and</strong> found that on-line dn=dc measurements were in good<br />

agreement with <strong>of</strong>f-line measurements. Furthermore, these investigators<br />

demonstrated the use <strong>of</strong> gradient elution high-performance liquid chromatography<br />

(HPLC) with an on-line light-scattering detector <strong>and</strong> applied this<br />

technique to examine aggregation <strong>of</strong> bovine alkaline phosphate (186,210),<br />

ribonuclease A(186), lysozyme (186), <strong>and</strong> pituitary <strong>and</strong> recombinant human<br />

growth hormones (184).<br />

Dollinger et al. (211) used an HPLC fluorimeter as a908 light-scattering<br />

detector for proteins analyzed by reversed-phase HPLC. The excitation <strong>and</strong><br />

emission wavelengths were both set to 467 nm. Because <strong>of</strong> the small size <strong>of</strong> the<br />

proteins, there was no measurable scattering asymmetry for molecular weights<br />

below 1 10 6 g/mol, <strong>and</strong> the scattered intensity at 908 was found to be<br />

proportional to molecular weight. The light-scattering method was further<br />

simplified, in this case, by assuming that the second virial coefficient was<br />

negligible under HPLC conditions <strong>and</strong> that dn=dc values for all proteins under<br />

similar chromatographic conditions were equal. Figure 13 shows the LS <strong>and</strong> UV<br />

responses for lysozyme analyzed by reversed-phase HPLC. The double peaks have<br />

the same molecular weight <strong>and</strong> correspond to different conformers rather than<br />

aggregates.<br />

© 2004 by Marcel Dekker, Inc.

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