Nitric oxide synthase and arginase (NOS/ARG)

Nitric oxide synthase (NOS) and arginase represent two distinct enzyme families that compete for L-arginine as a common substrate (Caldwell et al., 2018). The NOS family includes three isoforms: neuronal (nNOS/NOS1), inducible (iNOS/NOS2), and endothelial (eNOS/NOS3), which produce nitric oxide (NO) to regulate vascular tone and immune signaling (UniProt P29474, P35228, P29475). Arginase exists in two forms, ARG1 and ARG2, which hydrolyze L-arginine to urea and L-ornithine, primarily functioning in the urea cycle and polyamine synthesis (UniProt P05089, P78540). The reciprocal regulation of these enzymes is a critical determinant of NO bioavailability; increased arginase activity can lead to L-arginine deficiency, causing NOS uncoupling and oxidative stress (Durante et al., 2007). This imbalance is implicated in various pathologies, including hypertension, atherosclerosis, and asthma (Steppan et al., 2013). In the context of cancer, arginase produced by myeloid-derived suppressor cells (MDSCs) inhibits T-cell activation by depleting local L-arginine (NCBI PMC5864435). Therapeutic strategies include arginase inhibitors like numidargistat to enhance anti-tumor immunity and NOS modulators to treat cardiovascular or inflammatory conditions (ClinicalTrials.gov). Consequently, these enzymes are often studied together as a metabolic pivot point in health and disease.

Other names

NOS/ARG pathwayArginine metabolic enzymesL-arginine-ureahydrolase and Nitric-oxide synthase

Competitive inhibition of L-arginine metabolism; NOS inhibitors reduce nitric oxide production, while arginase inhibitors increase L-arginine availability for nitric oxide synthesis or decrease polyamine production.