Peroxidase-benzhydroxamic acid complexes: spectroscopic evidence that a Fe-H₂O distance of 2.6 Å can correspond to hexa-coordinate high-spin heme

Abstract

 Resonance Raman (RR) spectra have been obtained for single-crystal horseradish peroxidase isozyme C complexed with benzhydroxamic acid (BHA). The data are compared with those obtained in solution by both RR and electronic absorption spectroscopies at room and low (12–80 K) temperatures. Moreover, the analysis has been extended to the Coprinus cinereus peroxidase complexed with BHA. The results obtained for the two complexes are very similar and are consistent with the presence of an aqua six-coordinate high-spin heme. Therefore it can be concluded that despite the rather long Fe-H₂O distance of 2.6–2.7 Å found by X-ray crystallography in both complexes, the distal water molecule can still coordinate to the heme iron.