Figure 3.
The molybdenum site of the L subunit. (A) The Mo ion exhibits one hydroxo and two oxo ligands and is bound to MCD through its enedithiolene group. The second coordination sphere of the Mo ion is composed of the residues Gln240L, Glu763L, and S-selanyl-Cys388L. B and C show the active site together with the adjacent [2Fe–2S] cluster. Difference Fourier maps were calculated with the phases from the final model shifted by 90° (imaginary map) and with amplitudes from the Bijvoet differences at a wavelength λ1 = 1,7316 Å (B) shown in red and calculated with data obtained at a wavelength of λ2 = 0,9761 Å (C) shown in yellow. The maps are contoured at 3σ. Calculated f′′ values using the program absorb for selected free atoms are Fe: λ1, 3.9 e− and λ2, 1.5 e−; Se: λ1, 1.41 e− and λ2, 3.84 e−; S: λ1, 0.69 e− and λ2, 0.23 e−; Mo: λ1, 3.36 e− and λ2, 1.23 e−.