Some of the many pathways that have been proposed 1: Igarashi & Seefeldt,14 2: Barney,17 3: Smith,19 and Morrison,20 Also, the pockets observed in this work P: Proximal, M: Medial, and D: Distal pockets. Residues labels are given to provide a frame of reference and outline the channel path. The CO in the dynamics calculations follows the channel predicted by Igarashi (labeled 1 in the figure).