Antigenic Determinants in Human Hemoglobin: The α Polypeptide Chain

[摘要] Antigenic determinants in the α-chain from human hemoglobin A were located by using isolated α-chain tryptic peptides as inhibitors in the micro-complement fixation reaction of α-chain antigen and α-chain antibodies. Although the α-chain antigen was not in the native state, it shared antigenic determinants with native hemoglobin. Hemoglobin did not fix complement, but it did bind to the α-chain antibody and inhibited the homologous complement fixation reaction. The antisera also formed precipitin complexes with hemoglobins containing the α-chain.Three antigenic determinants in the α-chain were located as follows: a) the amino-terminal end, αTpI, amino acids 1 to 7, and αTpI,II, amino acids 1 to 11, inhibited the complement fixation reaction to 34% and 61%, respectively, (however, αTpII, amino acids 7 to 11, alone did not inhibit the reaction); b) αTpXI, amino acids 93 to 99, a part of the FG non-helical region and the G helix in the carboxy-terminal half of the chain inhibited to 15%; c) αTpXIII, amino acids 128 to 139, is at the carboxy-terminal end of the chain and is part of the H helix. This peptide inhibited to 31%.The phylogenetic associations of myoglobin and the α-chain of hemoglobin are further strengthened by the similar locations of antigenic determinants. Both have antigenic sites at the carboxy-terminal end of the chain, and a possible similarity in the region surrounding heme. They differ in the amino-terminal region which is an antigenic site in the α-chain. The antisera to myoglobin did not appear to contain antibodies to this area. Another difference resides in amino acids, 17 to 31 of the α-chain, where myoglobin has an antigenic determinant in the region extending from the end of the A helix into part of the B helix.

[学科分类] 生物科学（综合）