Hemoglobin derivatives

Oxyhemoglobin and deoxyhemoglobin
Oxyhemoglobin and deoxyhemoglobin Oxygen - carrying hemoglobin is referred to as oxyhemoglobin (oxyHb). Each Hb molecule can bind 4 molecules of oxygen. After the release of oxygen, we speak of deoxyhemoglobin (deoxyHb). In both forms, iron is divalent because only Fe II + -containing hemoglobin can reversibly bind and transport the oxygen molecule. Oxygenation of the hemoglobin molecule changes the electronic state of the Fe II + -hem complex, which results in a change in the color of the dark red hue typical of venous blood to the bright red color of arterial blood. In the human body, about 98.5%  of oxygen is bound to hemoglobin.

Carbaminohemoglobin
Carbaminohemoglobin is a hemoglobin to which CO 2 is bound. Carbon dioxide binds to the globin chain of hemoglobin. The binding of CO 2 to hemoglobin reduces the affinity of hemoglobin for oxygen.

Methemoglobin
Methemoglobin (metHb; also hemiglobin or ferihemoglobin  ) is characterized by the presence of ferric iron, which is formed by oxidation of ferrous iron in hemoglobin  . Methemoglobin loses its ability to reversibly bind oxygen. In its place, Fe III + binds a water molecule through the sixth coordination bond. The color of methemoglobin is chocolate brown.

Methemoglobin is also present physiologically in small amounts in erythrocytes (about 1–3% of the total hemoglobin concentration  ). This is mainly due to the effect of nitrite, which is formed from nitrates contained in food. The reverse reduction of methaemoglobin to hemoglobin is mainly ensured by NADH-dependent cytochrome-b 5 reductase (also methemoglobin reductase). A minor role is played by NADPH-dependent methemoglobin reductase, which is dependent on the supply of NADPH from the pentose cycle and on the presence of another electron transporter (eg flavin). Non-enzymatic mechanisms include the action of glutathione and ascorbic acid. Methemoglobinemia - origin and therapy Elevated blood levels of methaemoglobin are called methaemoglobinaemia. The causes are different:


 * Hereditary methaemoglobinaemia is usually caused by a congenital defect in NADH-dependent methaemoglobin reductase or the presence of abnormal hemoglobin M.
 * Acquired methaemoglobinaemia is the most common form of methaemoglobinaemia. May be caused by oxidizing agents  :


 * poisoning by certain substances ( nitrobenzene, aniline and its derivatives - eg some dyes),
 * by the action of some drugs (local anesthetics - benzocaine, then phenacetin , sulfonamides ),
 * increased content of nitrates and nitrites in water and food.

Newborns are particularly sensitive to the increased content of these substances due to the immaturity of the reduction systems and the increased proportion of fetal hemoglobin, which is more easily oxidized. Methaemoglobinaemia is manifested by cyanosis with a characteristic gray-brown tint and hypoxia. Part of the therapy of acquired methaemoglobinaemia is the administration of some reducing agents - methylene blue or ascorbic acid.

Carbonyl hemoglobin
Carbonylhemoglobin (COHb, carboxyhemoglobin ) is formed by the binding of carbon monoxide to hemoglobin. The bond formed is 250-300 times stronger than the oxygen bond. Carbonyl hemoglobin cannot transport oxygen and cellular hypoxia develops due to the blood 's reduced ability to carry oxygen. In excess oxygen, the binding of carbon monoxide to hemoglobin is reversible. Therefore, inhalation of O 2 is the most important in carbon monoxide poisoning.

COHb can also be found in small amounts in healthy people. For urban dwellers, values ​​of around 2% are evident; for heavy smokers, COHb can rise to as much as 10% of total hemoglobin. Staying in an environment containing 0.1% CO for several minutes can increase the carbonyl hemoglobin concentration to 50%.

Carbon monoxide is formed during the imperfect combustion of fuels, it is also contained in the exhaust gases and in smoke during fires in closed rooms. Hemoglobin saturation curve Carbonyl hemoglobin is crimson red; even people with severe carbon monoxide poisoning tend to have "healthy" pink skin. Compared to hemoglobin, carbonyl hemoglobin is more resistant to chemical influences, it changes more slowly due to the action of various agents.

Spectrophotometry of hemoglobin derivatives
Absorption spectra of hemoglobin and its derivatives Hemoglobin and its derivatives have characteristic absorption spectra in the visible region of light, which are used for their analysis and rapid identification. Significant absorption maxima in the range of 400–430 nm, the so-called Soret band, are typical for all hemoproteins. Other absorption peaks are significantly lower. Oxyhemoglobin is characterized by two incompletely separated maxima in the region of 540 and 578 nm. Deoxyhemoglobin has a single absorption maximum at 555 nm. The main absorption maximum of methaemoglobin is at 630 nm and the second faint peak at 500 nm is pH dependent. By reacting methemoglobin with potassium cyanide, the maximum disappears at 630 nm, as cyanomethemoglobin is formed. The decrease in absorbance at 630 nm is proportional to the methaemoglobin concentration. Cyanmethemoglobinshows a broad absorption maximum at 540 nm, which is used to determine blood hemoglobin concentration. The carbonyl hemoglobin spectrum is similar to that of oxyhemoglobin, but the position of the peaks is shifted toward lower wavelengths. Determination of carbonyl hemoglobin: Determination of carbonyl hemoglobin spectrophotometry Determination of carbonyl hemoglobin in the blood is one of the basic toxicological examinations. It is an objective criterion in the assessment of acute and chronic carbon monoxide poisoning.


 * Spectrophotometric evaluation . Carbonyl hemoglobin can be determined rapidly spectrophotometrically by subtracting the absorption maximum shift of the diluted blood from 586 nm  . The shift of the maximum in the spectrum depends on the ratio of COHb and O 2 Hb in the sample.
 * Reactions with tannin . As a guide, carbonyl hemoglobin can be determined by reaction with tannin or Ajatin (from about 10% COHb). Tannin forms a strawberry red precipitate in the presence of carbonyl hemoglobin. In the absence of carbonyl hemoglobin, the color of the precipitate is brownish gray.
 * Acid-base balance analyzers . The analysis of the most toxicologically important hemoglobin derivatives COHb and metHb is also enabled by modern acid-base balance analyzers, which have a built-in photometric system for their measurement.

Links
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Reference

 * 1) ↑ KITTNAR, Otomar and ET AL ..  Medical physiology. 1st edition. Prague: Grada, 2011. 790 pp. 131.  ISBN 978-80-247-3068-4.
 * 2) ↑ ŠVÍGLEROVÁ, Jitka. Hemoglobin  [online]. Last revision 2009-02-18, [cit. 2010-11-11]. < https://web.archive.org/web/20160416205421/http://wiki.lfp-studium.cz/index.php/Hemoglobin >.
 * 3) ↑ ŠVECOVÁ, D and D BÖHMER. Congenital and acquired methaemoglobinaemia and their treatment. Journal of Czech doctors. 1998, vol 137, pp. 168-170, ISSN 1803-6597.
 * 4) ↑ RICHARD, Alyce M, James H DIAZ and Alan David KAYE. Reexamining the risks of drinking-water nitrates on public health. Ochsner J [online] . 2014, vol. 14, no. 3, pp. 392-8, also available from < https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4171798/?tool=pubmed >. ISSN 1524-5012.
 * 5) ↑ XU, F, KS QUANDT and DE HULTQUIST. Characterization of NADPH-dependent methemoglobin reductase as a heme-binding protein present in erythrocytes and liver. Proc Natl Acad Sci USA [online] . 1992, vol 89, no. 6, pp. 2130-4, also available from < https://www.ncbi.nlm.nih.gov/pmc/articles/PMC48610/?tool=pubmed >. ISSN 0027-8424.
 * 6) ↑ CORTAZZO, Jessica A and Adam D LICHTMAN. Methemoglobinemia: a review and recommendations for management. J Cardiothorac Vasc Anesth [online] . 2014, vol 28, no. 4, pp. 1043-7, also available from < https://www.ncbi.nlm.nih.gov/pubmed/23953868 >. ISSN 1053-0770 (print), 1532-8422.
 * 7) ↑ LEDVINA, M. Rapid spectrophotometric determination of carbonylhemoglobin in blood. Biochem Clin Bohemoslov. 1987, vol 16, pp. 493-495, ISSN 0139-9608.