Analyzing protein-DNA complex by SEC

Questions about Multi-Angle Light Scattering coupled with Size-Exclusion Chromatography or Field-Flow Fractionation

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If I am analyzing a protein-DNA complex by SEC, should I use protein calibration standards or DNA calibration standards?
With SEC-MALS, you don’t need to use any molar mass calibration standards! The MALS detector directly measures the molar mass of the protein, DNA, or other macromolecule. The measurement is independent of the elution time and specific calibration standards. Whether your molecule has a different density or conformation, compared to your standard, and whether your molecule interacts with the column (thus influencing its elution time) does not matter for SEC-MALS.

[answer provided by Sophia Kenrick, Ph.D., Wyatt Technology]
Daniel Some, Ph.D.
Principal Scientist
Wyatt Technology Corp.
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You will, however, need to know the dn/dc values of the protein and DNA, and UV extinction coefficients at the measurement wavelength (260 or 280 nm, usually).

The dn/dc values of most proteins and DNA are universal to good approximation - 0.186 and 0.17, respectively. The extinction coefficients can be calculated from the sequence, though it is best to measure them.
Daniel Some, Ph.D.
Principal Scientist
Wyatt Technology Corp.
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