Side-chain selective and covalent labelling of proteins by organometallic complexes of heavy transition metals--possible application in radio-crystallography of proteins.

Organo-rhenium and organo-tungsten N-succinimidyl and N-sulfosuccinimidyl esters react at amino groups of proteins to form stable amide bonds between the protein and the heavy transition metal complexes. We show here that factors such as pH of the reaction medium and nature of the reagent (coordinating metal, surrounding ligands, type of ester) had a marked influence on the final number of coupled organometallic groups per protein molecule, defined as the coupling ratio. By operating with stoichiometric quantities of reagent with respect to the number of aqino groups, up to 30 organometallic groups were introduced into the model protein, bovine serum albumin (BSA).

Labeling of proteins by organometallic complexes of rhenium. (I). Synthesis and biological activity of the conjugates.

We describe herein a totally new pathway for the introduction of rhenium in the form of low oxidation state organometallic complexes covalently attached to various proteins. The synthesis of several rhenium conjugates takes advantage of the specificity of N-succinimidyl esters for amino residues. Conjugation experiments were carried out under various conditions, and analysis of the conjugates was performed by FT-IR spectroscopy.