Q. You want to study the biochemical properties of respiratory enzyme complexes required for oxidative phosphorylation. Your first goal is to measure proton pumping by the NADH dehydrogenase complex. You mix purified NADH dehydrogenase complex with phospholipids and a pH indicator dye that changes color at acidic pH, and you follow a protocol for making liposomes. After verifying that the protein complex was incorporated into liposomes, you put in NADH and incubate at 37°C. You are dismayed to view no color change in the pH indicator dye.

One lab partner says the result is not surprising, since you forgot to add a key component. What is this main component? Explain why it is significant.