Problem Set #11: Electron Transfer Proteins
and the Photosynthetic Reaction Center
To answer the following questions, you may use your class notes from 11/24, your text, other texts on reserve, the PDB, and the scientific literature, probably in that order.
1. Cytochrome c oxidase is a highly-conserved, vitally important enzyme that catalyzes the reduction of oxygen to water in the mitochondria:
4 e- + 4 H+ + O2 ˆ 2 H2O
Like most other membrane proteins but unlike porins, this membrane-bound enzyme has largely ___________________________ secondary structure.
The enzyme receives its electrons from a small, water-soluble alpha-helical heme electron-carrying protein called ______________________.
It consists of _________________ chains and _____________________ cofactors, including
two _________________________, two _______________________, and a __________________.
Cytochrome c oxidase breaks down oxygen to water without releasing superoxide. When cyt c oxidase fails to work properly, the superoxide is disarmed by ____________________________.
The catalytic work of cytochrome c oxidase is done by redox-active metal ions ______________ and ___________________.
In the process of catalysis, the protein helps to establish a proton gradient across the mitochondrial inner membrane, which is subsequently used to generate ATP by the enzyme _____________________.
The cartoon on the next page shows a proposed mechanism for electron transfer in cytochrome c oxidase. Using the crystallographically-determined structure of bovine heart cytochrome c oxidase (1occ, 1ocr, 1ocz. pdb, etc.) determine the distances over which electrons must move between cofactors. How do electrons move through the protein? Where do the protons used to make water come from, and how do they get to the active site?
2. What cofactors are present in the photosynthetic reaction center, what do they do, and how are they similar or different to cofactors we have discussed before?