Uncoupling - uncoupling

The energy transfer mechanism between the ETC and ATP synthesis can be uncoupled if the reverse flow of protons from the intermembrane space to the matrix is ​​allowed. This ineffective loss of the proton gradient transforms the energy stored in it into its less useful form - heat.

Heat is generally much less useful than, for example, ATP, but there are situations where the ability to produce heat can save life - for example, when an organism is exposed to cold temperatures.

Muscle shivering is a well-known heat-generating mechanism used by humans and other mammals. This process produces heat through inefficient energy transfer during muscle contraction. Newborns and many animals use a different method - uncoupling of the mitochondrial chain (uncoupling) = non-shivering thermogenesis.

Uncoupling the respiratory chain to produce heat takes place mainly in a special tissue called brown adipose tissue.

Brown fat:
 * is colored like this because it contains many mitochondria,
 * its role is simply to "waste" energy.

White fat:
 * stores energy.

Mitochondria of brown adipose tissue contain a special protein that forms a channel in the inner mitochondrial membrane and thus enables the transfer of electrons – UCP-1 (uncoupling protein-1, thermogenin). When brown adipose tissue is activated by noradrenaline (via β3-adrenergic receptors), it hydrolyzes its triacylglycerols and the released fatty acids provide energy for ETC and simultaneously activate UCP-1.

There are also other subtypes of UCP (UCP-2 to UCP-5) expressed in other tissues, but their function is still not fully understood.