FIGURE 6.

Models of open, closed, and blocked kinetic states. A, model for one of the blocked states based on the crystal structure of Trp-64(E7) deoxyMb (Protein Data Bank code 3OGB). B, hypothetical model of an open state based on the Trp(E7) βCO structure shown in D, in which the E7 indole side chain has moved further away from the porphyrin ring by rotation about the Cα–Cβ bond to an angle similar to that for the indole side chain in Trp(E7) deoxyMb (A). C, closed conformation observed in the structure of deoxy-α(Trp-58(E7))β(WT) HbA (Protein Data Bank code 3NMM). D, blocked conformer based on the observed structure of α(WT)β(Trp-63(E7)) HbCO with the ligand removed (Protein Data Bank code 3NL7) and blue sphere representing the water molecule interconnecting the indole nitrogen atom with the heme propionates. The color scheme is identical to that in Fig. 5.