Pseudospecificity of the acidic patch of plastocyanin for the interaction with cytochrome f.

The ionic strength dependence of the physiological electron-transfer reaction of plastocyanins (PCus) from a range of sources with a eukaryotic cytochrome f (cyt f) has been studied. The presence of an acidic patch on the surface of PCu is key to this interaction in higher plants, but minor modifications in this surface region have a limited effect. Surprisingly, a similarly small influence results from the repositioning of the acidic patch (as in the fern PCu). The only requirement of a plant PCu to ensure efficient interaction with its cyt f is the presence of acidic residues on the periphery of the protein's hydrophobic patch.