TECHNETIUM COORDINATION ABILITY OF CYSTEINE-CONTAINING PEPTIDES - X-RAY-ABSORPTION SPECTROSCOPY OF A TC-99 LABELED ENDOTHELIN DERIVATIVE

The coordination mode of a Tc-99-labelled endothelin derivative, ly-Gl y-Cys-Gly-Cys-Phe-(D-Trp)Leu-Asp-Ile-Ile-Trp, in solution was determin ed by X-ray absorption spectroscopy (XAS). XAS analysis revealed that coordination of the [TcO](3+) core is restricted to the sequence -Cys- Gly-Cys-. The preferred coordination by the cysteinyl thiol group prev ents involvement of any donor atom other than sulphur, thus forming pu rely S-coordinate 1:2 complexes. Two occurring Tc-99 complex species w ith identical coordination spheres were identified and seem likely to represent parallel and antiparallel peptide chain orientation isomers. (C) 1997 Elsevier Science Ltd.