EXAFS OF LOW SPIN FERRIC CENTER OF NITRILE HYDRATASE

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Greatly improved polarized Fe-EXAFS data have been obtained from frozen-hydrated single monolayers of yeast cytochrome c covalently tethered to the nonpolar surface of mixed-CH3/-SH (6:1) endgroup Self-Assembled Monolayers (SAM) chemisorbed onto silicon substrates. These data have been analyzed utilizing the EXAFS spectra calculated using FEFF7 and either a) the local atomic environment within 5A of the Fe-atom in the yeast cytochrome c crystal structure as a function of the angle between the heme plane and the monolayer plane or b) the lcoal atomic environment within 5A of the Fe-atom as time-averaged over the last 300 picoseconds of a 1 nanosecond Molecular Dynamics computer simulation of the hydrated tethered cytochrome c/SAM system. Both approaches provide an angle between the heme plane and the monolayer plane in good agreement with independent results from the optical linear dichroism of the heme groups electronic transitions while the second approach best accounts for all of the features of the experimental polarized EXAFS data ?i.e. both peak positions in k (A-1) Hand peak shapes as opposed to primarily peak positions?. Examination Hof the unpolarized EXAFS spectra calculated from periodically sampled H?i.e., every 50 picoseconds? instantaneous configurations occurring Hover the 1 nanosecond Molecular Dynamics simulation indicated that the Hlocal atomic environment within 5A of the Fe-atom characteristic of Hthe frozen-hydrated isotropic aqueous solution of yeast cytochrome c Hoccurs repeatedly, but infrequently within the simulated hydrated Htethered cytochrome c/SAM system.