... Additionally, there are two partiallyoccupied sulfate ions. One of them forms two hydro-gen bonds with the main chain nitrogen atoms of Asp74 (2.80 A ˚) and Ala67 (2.86 A ˚) and with a watermolecule ... group and within a van der Waals distance of a methine carbon atom (CHA) of the porphyrin ring. Inconsequence, Gln57 is capable of tuning the redoxpotential of the heme group [7,8].An insert of ... Crystallogr 56, 1577–1582.13 Akazaki H, Kawai F, Chida H, Matsumoto Y, Hiray-ama M, Hoshikawa K, Unzai S, Hakamata W, NishioT, Park SY et al. (2008) Cloning, expression and purifi-cation of...