Figure 2.

The metabolic pathway for L-arginine and L-citrulline obtained from food sources, urea cycle and NO biosynthesis (A); NO biosynthesis from L-arginine by eNOS promotes vasodilation by activating guanylate cyclase to form cGMP that, in turn, decreases Ca²⁺ within smooth muscle cells, diminishing vascular tone and leading to vasodilation (B). eNOS—endothelial nitric oxide synthase, BH₄—tetrahydrobiopterin, FAD—flavin adenine dinucleotide, FMN—flavin mononucleotide, GC—guanylate cyclase, GTP—guanosine triphosphate, cGMP—cyclic guanosine monophosphate, Ca²⁺—calcium ions.