Table 2. Comparison of heme-ligand parameters for DHP A and B.

Only the values for molecule A of the asymmetric unit are listed for both structures.

	DHP B	DHP A
Fe—His89 N∊2 (Å)	2.16	2.09
Fe—His55 N∊2† (Å)
Inside conformation (Å)	5.48 (5.41)‡	4.8
Outside conformation (Å)	9.8 (10.26)	—
Fe—water§ (Å)	2.15	2.2
Fe to pyrrole N plane (Å)	0.21	0.04
Fe–ligand tilt angle¶ (°)	15.4	10.8

^†In the DHP B structure the distal histidine is present in conformations both inside and outside the pocket, whereas in the metaquo structure of DHP A (PDB entry 2qfk) it is only found in the conformation inside the pocket.

^‡In the DHP B structure the distal histidine assumes two conformations when oriented both inside and outside the pocket.

^§Distances for water as the sixth coordination ligand of heme Fe are listed (see text).

^¶The tilt angle is defined as the angle between the heme perpendicular and the Fe—O bond (Vangberg et al., 1997 ▶).