A respiratory pigment is a metalloprotein that serves a variety of important functions, its main being O2 transport.
[2] Sipuncula, priapulida, some brachiopoda, and a single annelid genus [3] Hemoglobin, erythrocruorin, and chlorocruorin are all globins, iron-heme proteins with a common core.
Any of various coloured conjugated proteins, such as hemoglobin, occur in living organisms and function in oxygen transfer in cellular respiration.
[citation needed] The globin is thought to be a very ancient molecule, even acting as a molecular clock of sorts.
[10] Similar in function to hemoglobin, leghemoglobin contains trace amounts of iron, but it is primarily found in plant roots.
For example, there are copper-containing tyrosinases that play significant roles in immune defense, wound healing, and the arthropod's cuticle.