Table 1.

X-ray data collection, refinement, and metal occupancy statistics for tuna Fe:Zn-cyt c structures

Stoichiometry*	2Fe:1Zn	1Fe:2Zn
Residues	103 + 1 heme	103 + 1 heme
Water molecules	488	488
Symmetry group	P43	P43
Unit cell dimensions, Å	74.18 × 74.18 × 35.54	74.36 × 74.36 × 35.70
Resolution, Å	30.0–1.5	30.0–2.0
X-ray wavelength, Å	1.54	1.28
Completeness, %	89.0	81.7
〈I/σI〉†	19.3	17.1
Rsym, %‡	6.6	6.2
R, %§	22.9	22.0
Free R, %¶	25.1	24.4
rmsd bond, Å‖	0.008	0.008
rmsd angle, °‖	1.4	1.4
Fe:Zn occupancy**	0.68:0.32	0.39:0.61
Average temperature  factor, Å2
Main-chain atoms	12.58	18.08
Side-chain atoms	12.74	18.12
Water molecules	23.46	29.98
Metal–ligand bond  distances, Å
His-18	(2.00)‡‡ 2.00	2.00
Met-80	(2.27)‡‡ 2.44	2.50††

^*Approximate stoichiometry of the crystallization solution. 

^† Intensity signal-to-noise ratio. 

^‡ R_sym = ∑∑_j|I_j − 〈I〉|/∑∑_j|I_j|. 

^§ R = ∑∥F_obs| − |F_calc∥/∑|F_obs| for all reflections (no σ cutoff). 

^¶ Free R calculated against 8% of the reflections removed at random. 

^‖ Root-mean-square deviations (rmsd) from ideal bond and angle restraints. 

^**Relative occupancies of Fe and Zn as determined by multiwavelength anomalous diffraction experiments. For 2Fe:1Zn, different crystals were used for structure and metal-occupancy determinations. Values are averages of the two molecules in the asymmetric unit. 

^‡‡ Fe(III)-only cyt c (Protein Data Bank ID code 3CYT). 

^†† The increase in the Met-80 bond length with increasing Zn occupancy indicates that for Zn-only cyt c, d_Met-80 ≥ 2.50 Å.