UCP are mitochondrial transporter proteins that create proton leaks across the inner mitochondrial membrane, thus uncoupling oxidative phosphorylation from ATP synthesis. As a result, energy is dissipated in the form of heat. Acts as a dimer forming a proton channel. Widely expressed in adult human tissues, including tissues rich in macrophages. Most expressed in white adipose tissue and skeletal muscle. Genetic variations in UCP2 define the body mass index quantitative trait locus 4 (BMIQ4) [MIM:607447]. A common polymorphism in the promoter of UCP2 has been shown to be associated with a decreased risk of obesity in middle-aged individuals. Belongs to the mitochondrial carrier (TC 2.A.29) family.