Catalyzes the biosynthesis of guanidinoacetate, the immediate precursor of creatine. Creatine plays a vital role in energy metabolism in muscle tissues. May play a role in embryonic and central nervous system development (By similarity). glycine + L-arginine = guanidinoacetate + L-ornithine Amine and polyamine biosynthesis; creatine biosynthesis; creatine from L-arginine and glycine: step 1/2. Homodimer. Transiently induced by estrogen, with levels peaking an hour after hormone injection. Belongs to the amidinotransferase family. Truncated N-terminus.