Enables protein homodimerization activity. Acts upstream of or within several processes, including catecholamine metabolic process; serotonin metabolic process; and voluntary musculoskeletal movement. Located in mitochondrion. Is expressed in several structures, including alimentary system; heart; nervous system; sensory organ; and skeleton. Used to study Parkinson's disease. Human ortholog(s) of this gene implicated in dystonia and sepiapterin reductase deficiency. Orthologous to human SPR (sepiapterin reductase). [provided by Alliance of Genome Resources, Apr 2022]