PP: Thermogenin

Thermogenin is a protein found in the inner mitochondrial membrane in the adipose tissue of some animals. It allows protons to flow from the intermembrane space to the mitochondrial matrix. If thermogenin is present in large quantities, it will decrease the rate of ATP synthesis but increase the rate of oxygen consumption, which is a measure of electron transport chain activity. This is because the proton gradient cannot form if protons are allowed to flow back to the matrix and cannot be built up in the intermembrane space, and this proton gradient is what powers the synthesis of ATP. On the contrary, oxygen consumption will increase since the electron transport chain will continue to pump protons into the intermembrane space in an attempt to form a gradient. Thermogenin allows for heat production without the production of ATP, so it is present in human infants and hibernating bears, animals that require heat but not much ATP.