Figure 4.

Proposed structural model of the active site in Chlamydomonas and Synechocystis HbO₂. Only selective residues in the vicinity of the heme are shown. The model was built by using the structural coordinates of HbO₂ of Ascaris suum (1ash.pdb, Brookhaven Protein Data Bank). The dotted lines represent hydrogen bonds (thick line, strong hydrogen bond; thin line, weak hydrogen bond). The E10 helical positions (not shown here) are occupied by a Lys and a His, respectively, in Chlamydomonas and Synechocystis Hb.