GATM (Glycine amidinotransferase, mitochondrial) is a mitochondrial enzyme that belongs to the amidinotransferase family. This enzyme is involved in creatine biosynthesis, whereby it catalyzes the transfer of a guanido group from L-arginine to glycine, resulting in guanidinoacetic acid, the immediate precursor of creatine. Creatine plays a vital role in energy metabolism in muscle tissues.