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

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

-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 oxygen ...

complexes, which have a

molecular mass The molecular mass (''m'') is the mass of a given molecule: it is measured in daltons (Da or u). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The related quanti ...

greater than 3.5 million

Dalton Dalton may refer to: Science * Dalton (crater), a lunar crater * Dalton (program), chemistry software * Dalton (unit) (Da), the atomic mass unit * John Dalton, chemist, physicist and meteorologist Entertainment * Dalton (Buffyverse), minor cha ...

s. Both are sometimes called giant hemoglobin or hexagonal bilayer haemoglobin. They are found in many

annelid The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecol ...

s and

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

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

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

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 The dalton or unified atomic mass unit (symbols: Da or u) is a non-SI unit of mass widely used in physics and chemistry. It is defined as of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at re ...

myoglobin-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-oxid ...

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 Sabellidae. Common names include the Mediterranean fanworm, the feather duster worm, the European fan worm and the pencil worm.Branch, G.M.; Branch, M.L.; Griffiths, ...

'' 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 BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...

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 very large molecule important to biophysical processes, such as a protein or nucleic acid. It is composed of thousands of covalently bonded atoms. Many macromolecules are polymers of smaller molecules called monomers. The ...

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