The photocycle and the structure of iron containing bacteriorhodopsin ?a kinetic and M�ssbauer spectroscopy investigation

Bacteriorhodopsin (bR), converted by deionization to the blue form was reconstituted to the active purple membrane by the addition of Fe2+ or Fe3+ ions. 57Fe Mossbauer spectra of these samples were measured at different pH values (pH 3.9, pH 5.0 and pH 7.0) and at temperatures ranging from 4 K to 300 K. The hyperfine parameters reveal two iron environments with oxygen atoms in the neighbourhood of iron. Iron type 1 is in the 3+ high spin state. It is bound to acid side chains of the protein and/or the phosphate groups of the lipids. Iron type 2 is in the 2+ high spin state and is linked to carboxy groups of the protein in a rather unspecific way. Dynamics as measured by Mossbauer spectrosco…