FIG. 1.

Ribbon representation of O₂(II)Mb including the ferroprotoporphyrin IX moiety. Structural aspects of sperm whale O₂(II)Mb are shown. The distal histidine, proximal histidine, and ferroprotoporphyrin IX (heme) moiety are shown in stick representation. Each helix is labeled. The iron atom in the center of the heme ring and ligand O₂ are shown as spheres. The heme-6-propionate (H6P) group is to the left of the heme-7-propionate. The PDB structure 1MBO (51) was used to prepare the image shown using PyMOL software. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars. Mb, myoglobin; PDB, Protein Data Bank.