Evaluation of 1-fluoro-2-nitro-4-trimethylammoniobenzene iodide, a protein-solubilizing reagent.

The new protein reagent 1-fluoro-2-nitro-4-trimethylammoniobenzene iodide reacts with model amino acids to give derivatives that are very stable to hydrolysis. In a dimethyl sulphoxide-water medium it reacts rapidly (3h) with bovine insulin, and substitution occurs quantitatively at the N-terminal amino groups and at the in-amino groups of lysine residues. Two of the four tyrosine residues react, and it is assumed that these are the exposed groups leaving the buried groups unattacked. Unlike 1-fluoro-2,4-dinitrobenzene and related reagents, it imparts hydrophilic properties to the protein derivative, thus facilitating structural and other studies on the derivative. Circular-dichroism spectra of the modified insulin suggest that no conformational changes have occurred during reaction. These spectra also reveal the presence of an extrinsic Cotton effect at 410nm.