Uncoupling proteins: beyond brown adipose tissue.

Uncoupling protein, originally described in the inner mitochondrial membrane of brown adipose tissue, permits the oxidation of fuels without the generation of adenosine triphosphate (ATP). Closely related proteins have now been found in many other tissues and shown to be regulated by thyroid hormones and dietary factors. These uncoupling proteins may play a significant role in energy expenditure, with implications for the development of human obesity.