<unk> s (also spelled<unk> s) are respiratory proteins in the form of metalloproteins containing two copper atoms that reversibly bind a single oxygen molecule (O2). Oxygenation causes a color change between the colorless Cu(I) deoxygenated form and the blue Cu(II) oxygenated form.<unk> s carry oxygen in the blood of most molluscs, and some arthropods such as the horseshoe crab.  They are second only to hemoglobin in biological popularity of use in oxygen transport.
Hemocyanin
Hemin
Toxidrome
Methaemoglobin
Hemocoel
Avidin
Hemoglobin
Phanquinone