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. Ubiquitously expressed in adult tissues, with highest levels in muscle and intermediate levels in eye, heart, liver, stomach and testis. In stage 28 embryos, expression is higher in the dorsal and ventral parts of the trunk than in the head. In middle gastrulae, expression is highest around the yolk plug, while in stage 15 and tailbud stage embryos, expression is largely restricted to the region around the presumptive notochord and gut. Expressed during embryonic development from the mid-gastrula stage onwards. Belongs to the amidinotransferase family.