FIG. 3.

Mechanism for the formation of NO via eNOS catalysis after the binding of the coenzyme tetrahydrobiopterin (H₄B). The heme iron (Fe) is the major catalytic site and represents NOS3 here. NOS3 undergoes a series of redox reactions. Arg represents l-arginine, and NOHA represents Nω-hydroxyl-l-arginine. Parentheses around H₄B, H₄B^+•, or H₃B^• mean that that species is bound to the enzyme. NO is released from Fe³⁺NO. All three NOS isoforms share a similar catalytic mechanism. [Adapted from (66, 85).]