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. Author manuscript; available in PMC: 2012 May 10.
Published in final edited form as: J Am Chem Soc. 2011 Apr 14;133(18):6968–6977. doi: 10.1021/ja107052p

Figure 9.

Figure 9

Two-dimensional contour representation of the ground state free energy surface for the ternary complex and radical pair formation and separation in EAL as a function of chemical (Co-C bond cleavage) and protein configuration coordinates. The two minima represent the ternary complex [Co(III)Ad] and the cob(II)alamin-5′-deoxyadenosyl radical pair [Co(II)Ad•] states. The one-dimensional trajectory for photolysis (Path 1) is represented by a horizontal bold arrow. The trajectory for the native thermal Co-C bond cleavage is represented by the diagonal bold arrow (Path 2). A representative position of the free energy minimum for the holo-EAL state is given by the region marked “A.” The region, “B,” marks a representative position for the free energy minimum of a protein state, that might be obtained by a simple substrate binding-induced switch of the holo-EAL protein configuration to one that favors prompt stabilization of the photoproduct radical pair.