To help scientists achieve a better understanding of how CcO works, Collman and his colleagues have built a new model of the enzyme's active site-a region on the protein's surface where chemical reactions occur. According to Collman, this new model might eventually help researchers gain insights into the causes of cancer and other major diseases, and might even prove useful in the development of new forms of alternative energy. The team's findings appear in the March 16 issue of the journal Science.
Many organisms, including humans, derive their energy from tiny organelles in cells known as mitochondria. Embedded in the membrane of each mitochondrion is a structure called the electron transport chain, which produces adenosine triphosphate (ATP), a molecule that is the source of the cell's energy. The transport chain is made up of a series of proteins known as electron carriers. Each carrier receives electrons from the preceding one, then transfers them down the chain. The final receptor of the electrons is a molecule of oxygen that is transformed into water and, in the process, generates energy in the form of ATP and heat.
CcO is the last electron carrier in the transport chain. It receives four electrons from the other carriers and transfers the electrons to the molecule of oxygen, converting it into two molecules of water.
"CcO has to behave perfectly," Collman said. "If it adds less than four electrons, it can produce partially reduced oxygen molecules, and thes