Heme in chlorocruorin, the source of its unique green color.
Erythrocruorin (from Greekeruthros "red" + Latincruor "blood"), and the similarchlorocruorin (from Greekkhlōros "green" + Latincruor "blood"), are largeoxygen-carryinghemeproteincomplexes, which have amolecular mass greater than 3.5 milliondaltons.[1] Both are sometimes calledgiant hemoglobin orhexagonal bilayer haemoglobin. They are found in manyannelids andarthropods (including some insects).[2]
Two structures of erythrocruorin have been resolved. The protein is a highly symmetric assembly made from heme-bindingglobins and unique linker proteins.[1][6]
The only significant difference between chlorocruorin and erythrocruorin is that chlorocruorin carries an abnormal heme group structure. Both contain many 16–17 kDamyoglobin-like subunits arranged in a giant complex of over a hundred subunits with interlinking proteins as well with a total weight exceeding 3600 kDa.[6]
Giant hemoglobin is composed of multiple heme-containingglobin chains and linker (InterPro: IPR031639) chains. Each species have different amounts of genes for these chains. For example, while aLamellibrachia sp. has four kinds of globin chains and two kinds of linker chains,Sabella spallanzanii has three globin chains and three linker chains.[6] The exact stoichiometric ratios and arrangement is unknown, but is thought to resemble that of erythocrorins.
Erythrocruorin has a weaker affinity for oxygen than that of mosthemoglobins. Adichromatic compound, chlorocruorin is noted for appearing green in dilute solutions, though it appears light red when found in concentrated solutions.[7][8][9]
This enormousmacromolecule is typically found free floating in the plasma, and not contained within red blood cells.[6][10]
^Lamy JN, Green BN, Toulmond A, Wall JS, Weber RE, Vinogradov SN (19 December 1996). "Giant Hexagonal Bilayer Hemoglobins".Chem Rev.96 (8):3113–3124.doi:10.1021/cr9600058.PMID11848854.
