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. 2021 Apr 16;9(4):432. doi: 10.3390/biomedicines9040432

Figure 2.

Figure 2

Molecular basis of nitric oxide (NO) reduction in erectile dysfunction. (Bullet 1) Superoxide (O2−) inactivates NO to form peroxynitrite (ONOO−). Peroxynitrite attacks and destroys tetrahydrobiopterin (BH4), a critical cofactor in NO synthesis. (Bullet 2) Advanced glycation end products (AGEs) promote superoxide formation, as well as directly inactivate NO. (Bullet 3) Arginase II degrades L-arginine, a substrate required for NO synthesis. (Bullet 4) Androgen deficiency reduces the expression of the endothelial isoform of NO synthase (eNOS). (Bullet 5) Rho-kinase reduces expression and phosphorylation of eNOS, which is required for its full activation. P = eNOS phosphorylation.