BOND VALENCE SUM ANALYSIS OF METAL-LIGAND BOND LENGTHS IN METALLOENZYMES AND MODEL COMPLEXES .2. REFINED DISTANCES AND OTHER ENZYMES

The bond valence sum (BVS) method is further applied to metalloenzyme active sites. When a particular coordination model is assumed, the BVS method allows for oxidation states of metal ions in metalloproteins to be determined from metal-ligand bond distances measured using extended X-ray absorption fine structure (EXAFS) analysis. Thus, the BVS can be used to determine the compatibility between a given coordination model and a particular oxidation state. A new procedure for calculating r0 values on which BVS's are based is presented. This procedure allows for calculation of r0 values on heteroleptic complexes and was used to determine a new set of r0 distances using complexes that more closely model the active sites of interest. In particular, the new distances allow for calculations involving vanadium, molybdenum, and nickel. New calculations using EXAFS data on CO dehydrogenase, NiFe hydrogenase, manganese catalase, sulfite oxidase, MoFe nitrogenase, and VFe nitrogenase are presented. The interplay between oxidation state and coordination geometry can be quantitatively assessed using the BVS method.