Hydrogen exchange in hydrated films of proteins. Application to the E. coli lac repressor core

An original easy method of hydrogen to deuterium exchange in hydrated films of proteins, followed by infrared absorption measurements, is described and applied to films of the E. coli lac repressor core, in order to examine the effect of isopropyl-beta-D-thiogalactoside (IPTG) binding. An estimation of about 25% alpha helical structure in this protein fragment is deduced from the exchange curve. The binding of IPTG to the core does not affect the exchange curve within the experimental error limits.