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. Strongly expressed in neurons and glia of the brain, the lamina propria, submucosa and serosa of the small intestine, in oocytes and on the fringes of the pancreas. Not expressed in the retina, eye lens, heart or bulbus arteriosus. Expressed in the yolk syncytial layer in gastrula stage embryos, in the yolk syncytial layer and mature somites in early segmentation embryos and in the yolk syncytial layer and the liver of long-pec stage (48 hours post-fertilization) embryos. Widely expressed during maturation of oocytes. Also expressed in embryos from gastrulation onwards in the yolk syncytial layer and somites. Expression declines in the somites, but is up-regulated in the yolk syncytial layer throughout embryonic development. Belongs to the amidinotransferase family.