The Effect of Removal of C-terminal Residues on Cooperative Interactions in Hemoglobin

Deoxyhemoglobin has a low affinity and oxy-hemoglobin a high affinity for oxygen. Since the latter is similar to that of the isolated ~ and fl chains, i t is thought that the low affinity of deoxyhemoglobin is a result of constraints imposed upon this form. Perutz (1970) has proposed that these constraints are the salt bridges involving the C-terminal residues of the ~ and fl chains dis-covered in the high resolution studies of human and horse deoxyhemoglobin (Muirhead and Greer, 1970; Bolton and Perutz, 1970). The salt bridges of the r162 chain involve the ~-carboxyl of Arg 141:% with both the s-amino group of Val 1 ~ 2 and the e-amino group of Lys 127 ~ e, and the guanidinium group of Arg 141: % with the carboxyl group of