Formate dehydrogenase molybdenum and tungsten sites—observation by EXAFS of structural differences

Preliminary EXAFS data has been collected on the molybdenum (K-edge) in C. pasteurianurn formate dehydrogenase and the tungsten (LHi-edge) in C. thermoaceticum formate dehydrogenase. In the presence of dithionite, the tungsten enzyme was devoid of W = O bonds, and exhibited average W-(O, N) and W-S bond lengths of 2.13 ± 0.03 and 2.39 + 0.03 A., respectively. In sharp contrast, he C. pasteurianum molybdenum site has three Mo = O bonds with an average bond length of 1.74 ± 0.03 A.. It is also the first molybdenum enzyme found lacking Mo-S bonds, and does not appear to be redox active in the presence of formate or dithionite. Model compounds WO2(8-hydroxyquinoline)2 = WO2(ox)2, and WO2(8 mercaptoquinoline)2 = WO2(tox)2, were also examined. Respective predicted bond lengths for WO2(ox)2 and WO2(tox)2 were W = O of 1.71, 1.73.~, ; W-N of 2.31, 2.29 A.; W-O or W-S of 1.92 or 2.40 A, with estimated uncertainties of ±0.03 A. The enzymes wh ich cata lyze the revers ib le ox idat ion o f fo rmate to carbon d iox ide