Enables long-chain fatty acid binding activity; oxidative phosphorylation uncoupler activity; and purine ribonucleotide binding activity. Involved in several processes, including cellular response to cold; diet induced thermogenesis; and positive regulation of cold-induced thermogenesis. Acts upstream of or within brown fat cell differentiation and regulation of transcription by RNA polymerase II. Located in mitochondrial inner membrane. Is expressed in several structures, including adipose tissue; adrenal gland; submandibular gland; testis; and thymus. Human ortholog(s) of this gene implicated in hypertension and type 2 diabetes mellitus. Orthologous to human UCP1 (uncoupling protein 1). [provided by Alliance of Genome Resources, Apr 2022]