Fluorine nuclear magnetic resonance studies of trifluoroacetylinsulin derivatives. Effects of salts and denaturants.

19F nuclear magnetic resonance spectroscopy has been used to study the effects of salts and denaturants on the structure and aggregation properties of several trifluoroacetyl derivatives of insulin. This technique has been shown to be a powerful tool in the study of specific sites on the protein molecule. Circular dichroic and sedimentation velocity studies were also carried out to aid in the interpretation of the magnetic resonance data. At pH 6.8 Zn2+ had no effect on the 19F magnetic resonance spectrum, however, citrate and acetate ions significantly sharpened the signal from the trifluoroacetyl probe at the N-terminal end (glycine A-1) of the insulin A chain. No alterations were observed in the S20,W value of circular dichroic spectra, suggesting that the probe had gained a considerable degree of motional freedom without changes in aggregation or conformational properties. In the absence of perturbants the trifluoroacetyl group on glycine A-1 showed considerably more motional freedom than on phenylalanine B-1. Guanidine hydrochloride and sodium dodecyl sulfate were used to study the unfolding of several trifluoroacetylinsulin derivatives. The results suggested differential alterations in the environments of the probes located at glycine A-1, phenylalanine B-1, and lysine B-29 in the insulin molecule as the concentration of perturbant was increased.