Hemoglobin

Literature References: Hb; ferrohemoglobin. The major component of red blood cells which transports oxygen from the lungs to body tissues and facilitates the return transport of carbon dioxide. Mammalian hemoglobins have mol wts of about 64,500. Composed of four peptide chains called globins, each of which is bound to a heme, q.q.v. Normal human hemoglobin is composed of a pair of two identical chains. Iron is coordinated to four pyrrole nitrogens of protoporphyrin IX, and to an imidazole nitrogen of a histidine residue from the globin side of the porphyrin. The sixth coordination position is available for binding with oxygen and other small molecules. Called oxyhemoglobin, HbO2, in the oxygenated form and carboxyhemoglobin, HbCO, when oxygen is displaced by carbon monoxide. Binds reversibly with oxygen while the heme iron remains in the ferrous state. Autoxidation is prevented by the cover of hydrophobic groups of the globin. When the iron in hemoglobin is oxidized from the ferrous to the ferric state the compd is called methemoglobin, q.v. and is accompanied by a loss of oxygen-binding capacity. Hemoglobin is usually prepd by separating the red blood corpuscles from the lighter plasma by centrifuging; the plasma is siphoned off, and on adding ether to the blood corpuscle paste, the cells burst. After another centrifugation to remove the ruptured cell envelopes, a clear red soln of the protein is obtained [Fieser, Fieser, Org. Chem. (New York, 3rd ed., 1956) p 455]. Prepn of cryst HbO2 from washed horse or dog erythrocytes: Heidelberger, J. Biol. Chem. 53, 31 (1922); see also Ferry, Green, ibid. 81, 175 (1929); from human blood: Drabkin, ibid. 164, 703 (1946). Structure studies: Muirhead, Perutz, Nature 199, 633 (1963); Perutz et al., ibid. 219, 131 (1968); Perutz, Proc. Roy. Soc. London 173B, 113 (1969). Respiratory properties of hemoglobin and its function as a carrier of oxygen and carbon dioxide: Peters, Van Slyke, Quantitative Clinical Chemistry vol. I (Baltimore, 1932). Mechanism of action: Arnone in Annu. Rev. Med. 25, 123-130 (1974). Reviews: Lemberg, Legge, Hematin Compounds and Bile Pigments (New York, 1949); F. W. Sunderman, Hemoglobin: its Precursors and Metabolites (Lippincott, Philadelphia, 1964); H. Lehmann, R. G. Huntsman, Man's Hemoglobins (ibid. 1966); Huisman, Schroeder, New Aspects of the Structure, Function, and Synthesis of Hemoglobins (Butterworth, London, 1971); M. F. Perutz, Annu. Rev. Biochem. 48, 327-386 (1979); G. Fermi, M. F. Perutz, Haemoglobin & Myoglobin (Oxford Univ. Press, New York, 1982) 104 pp; R. E. Dickerson, I. Geis, Hemoglobin: Structure, Function, Evolution, and Pathology (Benjamin-Cummings, Menlo Park, Calif., 1983) 176 pp.

Properties: Crystal form, solubility, affinity for oxygen, absorption spectra differ quantitatively in hemoglobins of different species, due to the variation in amino acid sequence of the protein moiety since the same heme group is present in all vertebrate and many invertebrate hemoglobins. Human HbO2 = tetragonal crystals; horse HbO2 = orthorhombic crystals from citrated blood, monoclinic crystals from oxalated blood. Absorption spectra, see Lemberg, Legge, loc. cit., 228. Oxyhemoglobin is an article of commerce where it is called hemoglobin. Brownish-red powder or scales. Soluble in about 7 parts water, slowly sol in glycerol.