1H and 19F nuclear magnetic resonance investigation of the active site of catalase

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Abstract
In order to pinpoint the location of a water molecule in the vicinity of the active site of catalase water-proton relaxation times have been determined for aqueous solutions of beef-liver catalase in the presence and absence of fluoride and formate. Additionally, fluorine relaxation times have been measured for solutions containing sodium fluoride. Surprisingly, it is shown that water does not coordinate directly to the haem active centre. Instead, there is evidence for the presence of a water molecule strategically situated some 3.6–3.8 Å away from the haem iron and hydrogen-bonded to neighbouring amino-acid residues, histidine and asparagine. This may have important consequences mechanistically, since its replacement by peroxide allows direct coordination of peroxide to the haem group and simultaneous interactions with neighbouring amino-acid residues may facilitate efficient peroxide bond cleavage.