Erythrocruorin (from Greek ''eruthros'' "red" + Latin ''cruor'' "blood"), and the similar chlorocruorin (from Greek ''khlōros'' "green" + Latin ''cruor'' "blood"), are large

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

-carrying

hemeprotein A hemeprotein (or haemprotein; also hemoprotein or haemoprotein), or heme protein, is a protein that contains a heme prosthetic group. They are a very large class of metalloproteins. The heme group confers functionality, which can include oxyge ...

complexes, which have a

molecular mass The molecular mass () is the mass of a given molecule, often expressed in units of daltons (Da). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The derived quan ...

greater than 3.5 million daltons. Both are sometimes called giant hemoglobin or hexagonal bilayer haemoglobin. They are found in many

annelid The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to vario ...

s and

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

s (including some insects). Chlorocruorin is particularly found in certain marine

polychaete Polychaeta () is a paraphyletic class of generally marine Annelid, annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called c ...

Structure

Two structures of erythrocruorin have been resolved. The protein is a highly symmetric assembly made from heme-binding

globin The globins are a superfamily of heme-containing globular proteins, involved in binding and/or transporting oxygen. These proteins all incorporate the globin fold, a series of eight alpha helical segments. Two prominent members include myo ...

s and unique linker proteins. The only significant difference between chlorocruorin and erythrocruorin is that chlorocruorin carries an abnormal heme group structure. Both contain many 16–17 kDa

myoglobin Myoglobin (symbol Mb or MB) is an iron- and oxygen-binding protein found in the cardiac and skeletal muscle, skeletal Muscle, muscle tissue of vertebrates in general and in almost all mammals. Myoglobin is distantly related to hemoglobin. Compar ...

-like subunits arranged in a giant complex of over a hundred subunits with interlinking proteins as well with a total weight exceeding 3600 kDa. Giant hemoglobin is composed of multiple heme-containing

chains and linker () chains. Each species have different amounts of genes for these chains. For example, while a ''

Lamellibrachia ''Lamellibrachia'' is a genus of tube worms related to the giant tube worm, '' Riftia pachyptila''. They live at deep-sea cold seeps where hydrocarbons (oil and methane) leak out of the seafloor, and are entirely reliant on internal, sulfide-oxi ...

sp.'' has four kinds of globin chains and two kinds of linker chains, ''

Sabella spallanzanii ''Sabella spallanzanii'' is a species of marine polychaete worms in the Family (biology), family Sabellidae. Common names include the Mediterranean fanworm, the feather duster worm, the European fan worm and the pencil worm.Branch, G.M.; Branch, ...

'' has three globin chains and three linker chains. The exact stoichiometric ratios and arrangement is unknown, but is thought to resemble that of erythocrorins.

Properties

Erythrocruorin has a weaker affinity for oxygen than that of most

hemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...

s. A dichromatic compound, chlorocruorin is noted for appearing green in dilute solutions, though it appears light red when found in concentrated solutions. This enormous

macromolecule A macromolecule is a "molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass." Polymers are physi ...

is typically found free floating in the plasma, and not contained within red blood cells.

References

External links

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RSDB Molecule of the Month: 159 Erythrocruorin
Proteins Respiratory pigments Hemoproteins {{protein-stub