Table 2.

Calculated Interaction Energy of the Heme as a Function of Alpha, the Orientation of the Histidine Ligand

[Kcal/mol]	AH/DH	A−/DH	A−/D−
Total interaction energy
Maximum	−15.6	−20.6	−17.2
Minimum	−18.2	−24.0	−21.3
Electrostatic interaction energy
Maximum	−1.2	−6.2	−2.7
Minimum	−1.9	−7.8	−4.9
Parallel (alpha 0°) – pos. 1	−1.7	−7.6	−4.9
Parallel (alpha 90°) – pos. 2	−1.2	−6.4	−2.7
Perpendicular (alpha 0° & 90°) – pos. 3	−1.5	−7.0	−3.8

The total and the electrostatic interaction energies between the imidazole ligands and the heme. The plotted interactions in Figure 4 show only the ligand orientation energy difference for the sake of clarity. A is the propionate attached to the heme ring A and D to ring D. The propionatic acids are referred to as AH and DH, while the propionate is referred to as A⁻ and D⁻.