Light and photobiomodulation
Cytochrome c oxidase (CCO)
Cytochrome c oxidase (CCO), also called complex IV, is the last enzyme in the mitochondrial respiratory chain. It transfers electrons to oxygen to make water, a step that drives ATP production. It also absorbs red and near infrared light, which is why it is the proposed target of photobiomodulation.
Also called CCO, complex IV, cytochrome c oxidase complex IV
The settled biochemistry. CCO sits at the end of the electron transport chain in the inner mitochondrial membrane. It accepts electrons from cytochrome c and passes them to molecular oxygen, forming water, while helping pump protons across the membrane. That proton gradient is what ATP synthase uses to make ATP. This part is textbook.
The light connection. CCO contains copper and haem centres whose absorption bands fall in the red and near infrared. Tiina Karu’s group mapped action spectra for a light-induced cellular effect and found peaks at 619, 657, 675, 740, 760 and 820 nm, concluding that a photoacceptor — “supposedly cytochrome c oxidase” — was responsible (Lasers in Surgery and Medicine, 2005).
What has been shown, and where. Increased CCO activity and increased ATP following red or near infrared exposure has been reported repeatedly in cultured cells and in animal tissue.
How it is usually put. CCO is the leading candidate for the molecule that absorbs red and near infrared light in tissue.
Why it matters here
CCO is the molecule named whenever someone explains how red light is proposed to work. It is the leading candidate for what absorbs the light, and the step from there to an effect you would notice is still being researched.