The good news is that CcO rarely fails, said Stanford postdoctoral fellow Neal K. Devaraj, whose doctoral dissertation was the basis of the Science paper. According to Devaraj, CcO has more than 99 percent efficiency in transforming oxygen into water.
To understand why CcO is so efficient, Collman's group, led by Stanford research associate Richard Decreau, created an artificial version of the enzyme active site using organic compounds as building materials. The imitation site, which involves an elaborate sequence of 32 chemical steps, was built from scratch and took several years to develop.
The site contains the three active centers found in the naturally occurring enzyme: an organic molecule called phenol, an iron atom and a copper atom. Working together, these three centers provide the four electrons necessary to transform oxygen into water. "How all four electrons are added to oxygen has always been mysterious," Collman said. "Very few people study it. It's quite complex, and it's been broadly ignored."
Each electron is brought to the enzyme one at a time, Collman said: "It's like a bucket brigade in a Western movie." But the electrons are consumed too fast to study individually, he noted. Therefore, the researchers had to invent a technique that supplied electrons to their enzyme model in a slow and continuous way. They solved the problem by attaching the model to a liquid crystalline film on a gold electrode, which provided a nonstop supply of electrons to the model as it transformed oxygen molecules into water-a process called steady turnover.
"The biochemists that study the enzyme typically study single turnover," Collman said. "They let the enzyme have only one oxygen molecule and watch wh