Monomeric globin with a bis-histidyl six-coordinate heme-iron atom through which it can bind dioxygen, carbon monoxide and nitric oxide (PubMed:11473128, PubMed:12962627, PubMed:24699645). Could help transport oxygen and increase its availability to the metabolically active neuronal tissues, though its low quantity in tissues as well as its high affinity for dioxygen, which may limit its oxygen-releasing ability, argue against it (PubMed:11473128, PubMed:12860983, PubMed:12962627, PubMed:24699645). The ferrous/deoxygenated form exhibits a nitrite reductase activity and it could produce nitric oxide which in turn inhibits cellular respiration in response to hypoxia (PubMed:21296891). In its ferrous/deoxygenated state, it may also exhibit GDI (Guanine nucleotide Dissociation Inhibitor) activity toward heterotrimeric G-alpha proteins, thereby regulating signal transduction to facilitate neuroprotective responses in the wake of hypoxia and associated oxidative stress (PubMed:12860983, PubMed:18302932). {ECO:0000269|PubMed:11473128, ECO:0000269|PubMed:12860983, ECO:0000269|PubMed:12962627, ECO:0000269|PubMed:18302932, ECO:0000269|PubMed:21296891, ECO:0000269|PubMed:24699645}. This is the function of NGB (neuroglobin, Ensembl gene identifier ENSG00000165553).