Effects of potassium bromide disk formation on the infrared spectra of dried model proteins.

The most common method of sample preparation for Fourier transform infrared spectroscopic analysis of proteins in the solid state is compression after mixing with potassium bromide (KBr). Recently, questions have arisen as to whether proteins are conformationally altered by this process. In this study, the amide I Fourier transform infrared spectra of two model proteins, lysozyme and alpha-chymotrypsinogen, were measured before and after compression in KBr, and the effects of moisture exposure and the ratio of KBr to protein were examined. Contrary to earlier reports, compaction of the KBr/protein mixtures did not foster aggregation, and only minor apparent structural alterations were observed.