(a) Representation of the electrostatic surface potential of the homology model of NP7 (Knipp, Yang et al., 2007). Blue indicates positive charge potential and red indicates negative charge potential. The haem is indicated in van der Waals representation (green). The electrostatic surface potential was calculated and the figure was prepared with Swiss-PdbViewer (Guex & Peitsch, 1997) and the figure was rendered with POV-Ray (http://www.povray.org/
). (b) Reagents from the commercial Silver Bullets screen (Hampton Research) that successfully promoted crystallization of wt NP7 and NP7(E27V).