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. glycine + L-arginine = guanidinoacetate + L-ornithine Amine and polyamine biosynthesis; creatine biosynthesis; creatine from L-arginine and glycine: step 1/2. Homodimer. Expressed in kidney, brain, gonads, uterus, and embryonic head, chest and abdomen. Maternally expressed in the placenta and yolk sac of embryos. Expressed in a wide range of extraembryonic and embryonic tissues throughout development. Expressed at relatively low levels in mid-gestation stage embryos, with expression gradually increasing during embryonic development. Knockout mice do not manifest aminoaciduria or glucosuria. Belongs to the amidinotransferase family.