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

Abstract

Deoxyhemoglobin has a low affinity and oxyhemoglobin a high affinity for oxygen. Since the latter is similar to that of the isolated α and β chains, it 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 α and β chains discovered in the high resolution studies of human and horse deoxyhemoglobin (Muirhead and Greer, 1970; Bolton and Perutz, 1970). The salt bridges of the α chain involve the α-carboxyl of Arg 141α1 with both the α-amino group of Val 1α2 and the ε-amino group of Lys 127α2, and the guanidinium group of Arg 141α1 with the carboxyl group of Asp 126α2. The β chain salt bridges involve the α-carboxyl of His 14641β2 with the ε-amino group of Lys 40α1 and the imidazole group of His...