تسجيل الدخول

تسجيل

Regulation of Oxidative Phosphorylation:- Uncoupled Mitochondria in Brown Fat Produce Heat

المؤلف:  David L. Nelson، Michael M. Cox

المصدر:  Lehninger Principles of Biochemistry

الجزء والصفحة:  717

2026-06-23

44

Regulation of Oxidative Phosphorylation:- Uncoupled Mitochondria in Brown Fat Produce Heat

There is a remarkable and instructive exception to the general rule that respiration slows when the ATP supply is adequate. Most newborn mammals, including humans, have a type of adipose tissue called brown fat in which fuel oxidation serves not to produce ATP but to generate heat to keep the newborn warm. This specialized adipose tissue is brown because of the presence of large numbers of mitochondria and thus large amounts of cytochromes, whose heme groups are strong absorbers of visible light. The mitochondria of brown fat are like those of other mammalian cells in all respects, except that they have a unique protein in their inner membrane. Thermo genin, also called the uncoupling protein (Table 19–4), provides a path for protons to return to the matrix without passing through the FoF1 complex (Fig. 19–30).

FIGURE 19–30 Heat generation by uncoupled mitochondria. The un coupling protein (thermogenin) of brown fat mitochondria, by pro viding an alternative route for protons to reenter the mitochondrial matrix, causes the energy conserved by proton pumping to be dissipated as heat.

As a result of this short-circuiting of protons, the en ergy of oxidation is not conserved by ATP formation but is dissipated as heat, which contributes to maintaining the body temperature of the newborn. Hibernating animals also depend on uncoupled mitochondria of brown fat to generate heat during their long dormancy.