Figure 6. Overview of the possible metabolic pathways for arginine in RBC and their interaction with endothelial cells.

Enzymatic routes that can probably directly use or produce arginine, ornithine, urea, or citrulline in the RBC. Key to abbreviations: Arg: arginase; eNOS: endothelial nitric oxide synthase; NO: nitric oxide; NOS: nitric oxide synthase, and OCT: ornithine carbamoyl transferase.