CYGB encodes cytoglobin, a multifunctional globin protein with diverse cellular roles dependent on oxygen availability and redox conditions. Under normoxic conditions, CYGB functions as a potent nitric oxide dioxygenase, rapidly consuming NO to regulate vascular tone and blood pressure 1. The protein exhibits superoxide dismutase activity with rates approaching those of classical SOD enzymes (1.6 × 10⁸ M⁻¹·s⁻¹), protecting cells against oxidative stress through iron redox cycling 2. Under hypoxic conditions, CYGB can switch function to nitrite reductase, generating NO from nitrite 1. The gene is transcriptionally regulated by hypoxia-inducible factor-1 (HIF-1) through hypoxia-responsive elements at positions -141, -144, and -448, with expression increasing ~1.6-1.7-fold under hypoxic stress 3. CYGB shows high co-expression with neuronal nitric oxide synthase in hippocampus and is stress-responsive 4. In cancer contexts, CYGB can function as both tumor suppressor and oncogene depending on cellular context, with roles in clearing reactive oxygen species and influencing drug resistance 56. The gene produces multiple alternatively spliced isoforms, with the canonical V-1 isoform predominant in most tissues, though V-3 isoform is prevalent in liver tissues 7.