Literature References: a2-Globulins which combine with hemoglobin to form a weak peroxidase and which constitute about one-quarter of the a2-globulin fraction of human plasma: Jayle, Conas, Bull. Soc. Chim. Biol. 34, 65 (1952). Prepn: Herman-Boussier et al., ibid. 48, 817, 837 (1960). For each individual there are three genetic types of haptoglobins, each reacting identically with antibodies to each of the others. Structure of this serum glycoprotein is a tetramer composed of a- and b-polypeptide chains, the a-chain varying in the three phenotypes, the b-chains being identical. Amino acid sequence of a-chains: Black, Dixon, Nature 218, 736 (1968); Malchy, Dixon, Can. J. Biochem. 51, 321 (1973). C- and N-terminal sequences of the b-chain: Barnett et al., Biochemistry 11, 1189 (1972); A. Kurosky et al., Comp. Biochem. Physiol. 55B, 453 (1976); eidem, Biochemistry 15, 5326 (1976). Lowered levels of haptoglobins found in individuals with acute hepatitis and pernicious anemia. Review: Laurell, Grönvall, Adv. Clin. Chem. 5, 135-172 (1962). Monograph: Kirk, The Haptoglobin Groups in Man (S. Karger, New York, 1968) 77 pp. Review on genetics, biochemistry and physiology of human haptoglobins: J. Javid, Curr. Top. Hematol. 1, 151-192 (1978).