Spectrophotometric Evidence for Involvement of Aromatic Residues in the Interaction of Ferreascidin with Ferric Ion

The iron(III)-binding properties of pyrocatechol and ferreascidin, a blood protein isolated from a stolidobranch ascidian (Pyura stolonifera), have been characterized by spectrophotometric titrations with metal ion in the presence of nitrilotriacetate (NTA) to maintain solubility under the conditions used (pH 7.0, I0.2). Such studies of the model system have signified that the formation of the [Fe(NTA)(pyrocatechol)] 2- complex is governed by a stability constant of 10 32.5 M -2