Conformational states of hemoproteins by XANES: The mutant VR myoglobin

Abstract

We have measured the Fe K-XANES spectrum of a site directed double mutant myoglobin (VR Mb), where distal His(E7) is substituted by Val and Thr(E10) is substituted by Arg, at ESRF (Grenoble, France) in fluorescence mode, by using the ultra-pure Ge 13-element array detector by Canberra Industries. A change of the coordination symmetry at the Fe site induced by changing the two aminoacids in the distal side has been probed. Evidence that water is not bound to the iron site in the acid ferric myoglobin has been found. The result is in accord with previous NMR and optical spectroscopic data, suggesting that Arg(E10) is out of the heme pocket in acid ferric VR myoglobin.