A280 vs. protein assay?

Tom Tullius tom at radical.chm.jhu.edu
Thu Sep 15 09:45:24 EST 1994

We have encountered an unusual situation, and I was wondering if anyone
else has seen this. We are studying the monomer-dimer equilibrium of a
protein. Gel filtration chromatography of the (purified) protein sample
give two bands (detected at 280 nm) that have roughly equal integrals.
However, a Bio-Rad protein assay on each peak indicates that there is
approximately 20 times more protein present in the leading (high MW) peak
(presumably the dimer). Could dimerization somehow be "quenching" the
absorbance at 280 nm? Ideas or experience would be appreciated.

Tom Tullius
Department of Chemistry, Johns Hopkins University
tom at adical.chm.jhu.edu

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