MCEE is a 176 amino acid mitochondrial protein that belongs to the glyoxalase I family. MCEE catalyzes the interconversion of D- and L-methylmalonyl-CoA during the breakdown of branched chain amino acids. The gene encoding MCEE maps to human chromosome 2p13.3. Defects in the MCEE gene are the cause of an autosomal recessive disease known as methylmalonyl-CoA epimerase deficiency (MCEE deficiency), methylmalonyl-CoA racemase deficiency or methylmalonic aciduria type 3, which is characterized by mild to moderate methylmalonic aciduria.