Abstract
A research article in this week's issue by [ Yoshikawa et al ][1]. reports the structure of cytochrome c oxidase, an enzyme critical for a large fraction of aerobic respiration. In his commentary, Gennis explains how this structure relates to two previously published structures of the same enzyme and analyzes the controversial proton-pumping mechanism that the authors propose on the basis of their structure. [1]: http://www.sciencemag.org/cgi/content/short/280/5370/1723