This account reports recent developments of a functional model for the active site of cytochrome c oxidase (CcO). This CcO mimic not only performs the selective four-electron reduction of oxygen to water but also catalytically reduces oxygen using the biological one-electron reductant, cytochrome c. This functional model has been used to understand other biological reactions of CcO, for example, the interaction between the gaseous hormone, NO, and CcO. A mechanism for inactivating NO-CcO complexes is found to involve a reaction between oxygen and CUB. Moreover, NO is shown to be capable of protecting CcO from toxic inhibitors such as CN- and CO. Finally, this functional CcO model has been used to show how H2S could induce hibernation by reversibly inhibiting the oxygen binding step involved in respiration.