| RECENTLY IDENTIFIED VERTEBRATE GLOBINS
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| In addition to Mb and Hb, two new cytosolic members of the vertebrate globin family have been identified since 2000. Neuroglobin is expressed primarily in brain and other nerve tissues; cytoglobin (or histoglobin) is ubiquitously expressed. Both human proteins share only about 25% sequence iden
tity with Mb and Hb. Yet all key elements of the globin domain are present, including the proximal and distal His residues and a hydrophobic pocket in which heme is inserted. The O2 affinities of the monomeric neuroglobin and cytoglobin are similar to that of Mb. Recent evidence suggests an Mb-like role in O2 storage and diffusion in tissues such as the retina, adrenal cortex, and pituitary. Other possible functions include scavenging reactive oxygen species and sensing cellular O2 concentration.
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