The respiratory electron transport chain is the final set of steps in the production of adenosine tripohosphate (ATP), the main form of energy used by cells. The final complex in the chain, cytochrome c oxidase, couples electron transfer with pumping protons across the membrane, which creates the chemical gradient that drives the production of ATP. The transferred electrons are then used to reduce molecular oxygen to water. CuA is the initial electron acceptor in cytochrome c oxidase, and it consists of two copper ions bridged by two cysteines and ligated by two histidines, a methionine, and the carbonyl backbone of a nearby glutamine. The two ligating histidines are of particular interest as they may affect the ability of the center to accept electrons and could possibly be involved in the movement of protons through cytochrome c oxidase. To test if the ligating histidines are reactive to small molecules, the portion of cytochrome c oxidase from the bacteria Thermus thermophilus that contains the CuA site was reacted with the chemical modifier diethyl pyrocarbonate and observed through a variety of spectroscopic techniques at pH 5.0-9.0. The mutant protein with the non-ligating histidines removed was similarly tested. Results indicate that diethyl pyrocarbonate reacts with one ligating histidine in pH conditions close to those expected in the cell. The existence of the reactive ligating histidine suggests that this residue could play a role in a proton pumping pathway.

Investigating the reactivity of the ligating histidines at the CuA site of cytochrome c oxidase

253rd National Meeting (2017)

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