The invention provides methods and compositions relating to a novel family of UCP3 polypeptides and related nucleic acids involved in metabolic regulation. The polypeptides may be produced recombinantly from transformed host cells from the disclosed mUCP3 encoding nucleic acids or purified from mammalian cells. The invention provides isolated mUCP3 hybridization probes, knock-out/in constructs and primers capable of specifically hybridizing with the disclosed mUCP3 genes, mUCP3-specific binding agents such as specific antibodies, animals and cells modified with the subject mUCP3 nucleic acids, and methods of making and using the subject compositions in the biopharmaceutical industry.