Table 2. Refinement Statistics.

sample	SeMet CysOM	native CysOM	K204A CysM	native CysO
no. of non-H atoms	5529	6512	4648	1290
no. of protein atoms	5150	5454	4443	1266
no. of water atoms	349	1028	160	24
no. of ligand atoms	30	30	45	0
Rworking (%)a	19.2	17.6	19.0	19.5
Rfree (%)b	24.3	21.7	25.6	25.2
Ramachandran plot
most favored region (%)	89.7	91.7	89.4	89.0
additionally allowed regions (%)	7.5	7.9	8.6	11.0
generously allowed region (%)	1.9	0.3	1.6	0.0
disallowed region (%)	0.9	0.0	0.4	0.0
rms deviations from ideal
bonds (Å)	0.021	0.026	0.021	0.019
angles (deg)	2.0	2.2	2.0	2.0

^aR_working = Σ||F_o| − K|F_c||/Σ_hkl|F_o|, where F_o and F_c are the observed and calculated structure factors, respectively.

^bR_free was calculated using 5% of all reflections that were excluded at all stages of refinement.