Hemocyanins (also spelled haemocyanins) are respiratory
proteins in the form of metalloproteins containing two copperatoms that reversibly bind a single oxygenmolecule (O2). Oxygenation causes a colorchange between the colorless Cu(I) deoxygenated form and the blueCu(II) oxygenated form. Hemocyanins carry oxygen in the blood of most molluscs, and some arthropods such as the horseshoe crab. They are second only to hemoglobinin biological popularity of use in oxygen transport.Fact|date=October 2008
Although the respiratory function of hemocyanin is similar to that of hemoglobin, there are a significant number of differences in its molecular structure and mechanism. Whereas hemoglobin carries its
ironatoms in porphyrinrings ( hemegroups), the copperatoms of hemocyanin are bound as prosthetic groups coordinated by histidineresidues. Species using hemocyanin for oxygen transportation are commonly crustaceansliving in cold environments with low oxygen pressure. Under these circumstances hemoglobin oxygen transportation is less efficient than hemocyanin oxygen transportation.
Most hemocyanins bind with oxygen non-cooperatively and are roughly one-fourth as efficient as hemoglobin at transporting oxygen per amount of blood. Hemoglobin binds oxygen cooperatively due to steric conformation changes in the
protein complex, which increases hemoglobin's affinity for oxygen when partially oxygenated. In some hemocyanins of horseshoe crabs and some other species of arthropods, cooperative binding is observed, with Hill coefficients between 1.6-3. Hill constants vary depending on species and laboratory measurement settings. Hemoglobin for comparison has a Hill coefficient of usually 2.8-3. In these cases of cooperative bindinghemocyanin was arranged in protein sub-complexes of 6 subunits (hexamer) each with one oxygen binding site; binding of oxygen on one unit in the complex would increase the affinity of the neighboring units. Each hexamer complex was arranged together to form a larger complex of dozens of hexamers. In one study, cooperative binding was found to be dependent on hexamers being arranged together in the larger complex, suggesting cooperative binding between hexamers. Hemocyanin oxygen-binding profile is also affected by dissolve-salt ion levels and pH.
Hemocyanin is made of many individual subunit proteins, each of which contains two
copperatoms and can bind one oxygen molecule (O2). Each subunit weighs about 75 kilodaltons (kDa). Subunits may be arranged in dimers or hexamers depending on species, the dimer or hexamer complex is likewise arranged in chains or clusters in weights exceeding 1500 kDa. The subunits are usually , or heterogeneouswith two variant subunit types. Because of the large size of hemocyanin, it is usually found free-floating in the blood, unlike hemoglobin, which must be contained in cells because its small size would lead it to clog and damage blood-filtering organs such as the kidneys. This free-floating nature can allow for increased hemocyanin density over hemoglobin and increased oxygen carrying capacity. On the other hand, free-floating hemocyanin can increase viscosity and increase the energy expenditure needed to pump blood.
It is interesting to compare hemocyanin to the phenol oxidases (e.g. tyrosinase), homologous enzymes sharing its type 3 Cu active site coordination. Hemocyanin also exhibits phenol oxidase activity, but with slowed kinetics from greater steric bulk at the active site. Partial denaturation actually improves hemocyanin’s phenol oxidase activity by providing greater access to the active site. cite web|url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TCV-40W5V6F-J&_user=521824&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000059577&_version=1&_urlVersion=0&_userid=521824&md5=19f7d0f5a6ce73e94c9b9f9496a44504| title=Tyrosinase/catecholoxidase activity of hemocyanins: structural basis and molecular mechanism|accessdate= 2008-07-31|author= Decker|year= 2000|month= August|publisher= http://www.sciencedirect.com]
Spectroscopy of oxyhemocyanin shows several salient features:Fact|date=April 2007
Raman spectroscopyshows symmetric binding
UV-Vis spectroscopyshows strong absorbances at 350 and 580 nm.
# OxyHc is EPR-silent indicating the absence of unpaired electrons
Infrared spectroscopyshows ν(O-O) of 755 cm-1
(1) rules out a mononuclear peroxo complex(2) does not match with the UV-Vis spectra of mononuclear peroxo and
Kenneth Karlin's trans-peroxo models.cite journal | author = K. D. Karlin, R. W. Cruse, Y. Gultneh, A. Farooq, J. C. Hayes and J. Zubieta | title = Dioxygen-copper reactivity. Reversible binding of O2 and CO to a phenoxo-bridged dicopper(I) complex | year = 1987 | journal = J. Am. Chem. Soc.| volume = 109 | issue = 9 | pages = 2668–2679 | doi=10.1021/ja00243a019] (4) shows a considerably weaker O-O bond compared with Karlin's trans-peroxo model.
On the other hand,
Nobumasa Kitajima's model shows ν(O-O) of 741 cm-1 and UV-Vis absorbances at 349 and 551 nm, which agree with the experimental observations for oxyHc.cite journal | author = N. Kitajima, K. Fujisawa, C. Fujimoto, Y. Morooka, S. Hashimoto, T. Kitagawa, K. Toriumi, K. Tatsumi and A. Nakamura | title = A new model for dioxygen binding in hemocyanin. Synthesis, characterization, and molecular structure of the μ-η2:η2 peroxo dinuclear copper(II) complexes, [Cu(HB(3,5-R2pz)3)] 2(O2) (R = isopropyl and Ph) | year = 1992 | journal = J. Am. Chem. Soc.| volume = 114 | issue = 4 | pages = 1277–1291 | doi=10.1021/ja00030a025]
The weak O-O bond of oxyhemocyanin is because of metal-ligand backdonation into the σ* orbitals. The donation of electrons into the O-O antibonding orbitals weakens the O-O bond, giving a lower than expected infrared stretching frequency.
The hemocyanin found in "
Concholepas concholepas" blood has immunotherapeutic effects against bladder and prostate cancer. In a research made in 2006 micewere primed with C. concholepas before implantation of bladder tumor(MBT-2) cells. Mice treated with "C. concholepas" showed a significant antitumor effect as. The effects included prolonged survival, decreased tumor growth and incidence and lack of toxic effects. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B7XMT-4M818D9-3&_user=651519&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000035158&_version=1&_urlVersion=0&_userid=651519&md5=f00c10235b9a17349bd5b164a21ae54b#sec3] This Month in Investigative Urology, ScienceDirect]
Keyhole limpet hemocyanin
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Look at other dictionaries:
hemocyanin — hemocyanin. См. гемоцианин. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) … Молекулярная биология и генетика. Толковый словарь.
hemocyanin — [hē΄məsī′ə nin] n. [ HEMO + CYAN + IN1] a blue, oxygen carrying blood pigment containing copper, found in many arthropods and mollusks … English World dictionary
hemocyanin — noun Etymology: International Scientific Vocabulary hem + cyan + 1 in Date: 1885 a copper containing respiratory pigment in the circulatory fluid of various arthropods and mollusks … New Collegiate Dictionary
hemocyanin — n. [Gr. haima, blood; kyanos, dark blue] A blue oxygen carrying respiratory protein containing copper in the prosthetic group instead of iron; found in many invertebrate species … Dictionary of invertebrate zoology
hemocyanin — /hee meuh suy euh nin, hem euh /, n. Biochem. a blue, copper containing respiratory pigment in the plasma of many invertebrates. [1835 45; HEMO + CYAN 1 + IN2] * * * … Universalium
hemocyanin — noun a blue copper containing respiratory pigment (a metalloprotein) found in most molluscs, and some arthropods … Wiktionary
hemocyanin — An oxygen carrying pigment (molecular weights between 0.45 and 13 × 106) of lower sea animals (including molluscs and crustacea) and arthropods; copper is an essential component, but it contains no heme; used as an experimental antigen. * * *… … Medical dictionary
hemocyanin — Copper containing respiratory pigment in blood of malacostracans [Moore and McCormick, 1969]. (Class Malacostraca): Copper containing respiratory pigment in blood [McLaughlin, 1980] … Crustacea glossary
hemocyanin — he·mo·cy·a·nin … English syllables
hemocyanin — he•mo•cy•a•nin [[t]ˌhi məˈsaɪ ə nɪn[/t]] n. biochem. a blue copper containing pigment that transports oxygen in the blood of many mollusks, crustaceans, and other invertebrates • Etymology: 1835–45; hemo + Gkkýan(os)(see cyano ) + in I … From formal English to slang