Systematically cross-linked human hemoglobin: Functional effects of 10 angstrom spans between beta subunits at lysine-82

The structure and properties of hemoglobin are altered by the introduction of cross-links of defined structure between specific residues, The bis methyl phosphates and bis 3,5-dibromosalicylates of 4-carbuxy-trans-cinnamic acid as well as the bis methyl phosphate of 2,6-naphthalenedicarboxylic acid produce a 10 Angstrom cross-link between the epsilon-amino groups of each beta-lys-82 of human hemoglobin. The oxygen affinity of the modified proteins fits the correlation interpolated from those for shorter and longer cross-links. The oxygen binding curve shows a high degree of cooperativity. These results support the idea that the length of the semirigid cross-link in a structurally homogeneous series constrains the relaxation of the protein upon oxygen binding by a mechanism that is specifically reflected in the oxygen affinity, while interactions between hemes that affect cooperativity are not diminished.