Figure 1.
The environment of the proximal histidine in sperm whale Mb (5mbn, A) and Synechocystis rHb-R (1mwb, B). In A, the NδH group of His93 forms a hydrogen bond with Ser92 Oγ and Leu89 O. In B, the NδH group of His93 forms a hydrogen bond with Met66 O. The replacement of Ala69 with a Ser brings an O acceptor in the proximity of His70 NδH.