Investigation of protein structure by means of 19F-NMR. A study of hen egg-white lysozyme.

A 19F-labeled derivative of hen egg-white lysozyme, in which the six epsilon-amino groups are trifluoroacetylated (LF6), was prepared by reaction of lysozyme with S-ethyltrifluorothioacetate. The reaction mixture was fractionated by cation-exchange chromatography at pH 7.3. A comparison of the circular dichroic spectra and the activity towards Micrococcus lysodeikticus of both LF6 and native lysozyme reveals that the labeling causes no major conformational changes of the polypeptide backbone. Assignment of the six resonances present in the 19F-NMR spectrum of LF6 was accomplished by using a variety of techniques: specific chemical modifications, the effect of the inhibitor (GlcNAc)3, 19F-shift/pH information and relaxation parameters.