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Artifacts Associated with the Determination of Protein Secondary Structure by ATR-IR Spectroscopy

Volume 46, Number 4 (April 1992) Page 699-701

Jackson, Michael; Mantsch, Henry H.

The last decade has seen a dramatic increase in the application of FT-IR spectroscopy to biological problems. As well as transmission methods, many specialized techniques are increasingly being applied to biological structural studies, the most popular being ATR spectroscopy. While ATR-IR spectroscopy has been applied to conformational studies of lipids and membrane-associated proteins and peptides for some time, it has only recently been applied to soluble proteins. Two assumptions are made in the analysis of soluble proteins as films. First, it is assumed that drying of films does not result in irreversible structural alterations. Second, it is assumed that rehydration of the film results in the same degree of protein/solvent interaction as in solution, or that reduced solvent interaction in films does not produce structural alterations. In this note we compare spectra of representative proteins as films deposited on ATR elements and in solution. Our results show that significant differences are apparent between solution and film spectra.