Table 5.

Effects of azide on X-ray structures of resting oxidized CcO

The values indicate the occupancy of each multiple structure.

N3− concentration	Exposure	O2 reduction site		Heme a3		Helix X		PDB ID
		1 N3−	2 N3−	Structure A (nonshifted)	Structure B (shifted)	Conformer A (closed)	Conformer B (open)
20 mm	4 days	0.0	1.0	0.5	0.5	0.5	0.5	5Z84
	3 days	0.0	1.0	0.5	0.5	0.5	0.5	5Z86
	2 days	0.4	0.6	0.4	0.6	0.5	0.5	5ZCP
	2 daysa	0.0	1.0	0.5	0.5	0.5	0.5	5Z85
2 mm	2 daysa	0.7	0.3	0.7	0.3	0.8	0.2	5ZCO

^a Different batches of crystals were used for these experiments.