Modeling the molybdenum centers of the molybdenum hydroxylases

Making Moco: A Personal History

This contribution describes the path of my nearly forty-year quest to understand the special ligand coordinated to molybdenum and tungsten ions in their respective enzymes. Through this quest, I aimed to discover why nature did not simply use a methyl group on the dithiolene that chelates Mo and W but instead chose a complicated pyranopterin. My journey sought answers through the synthesis of model Mo compounds that allowed systematic investigations of the interactions between molybdenum and pterin and molybdenum and pterin-dithiolene and revealed special features of the pyranopterin dithiolene chelate bound to molybdenum.

Thiohydrazide complexes of molybdenum and their relevance to reduction of dinitrogen to ammonia

Tris(2-hydroxy thiobenzhydrazido)molybdenum(vi) can catalyze reduction of dinitrogen to ammonia in the presence of NaBH₄.

Coordination behavior and antifungicidal, antibacterial, and antifertility activities of dioxomolybdenum(VI) complexes of biologically active heterocyclic benzothiazolines

Synthesis, characterization, and structural aspects of a new class of dioxomolybdenum(VI) complexes with biologically active benzothiazolines, 2-(2-pyridyl) benzothiazoline, 2-(2-thienyl) benzothiazoline, 2-(2-furyl) benzothiazoline, 2-(3-indolyl) benzothiazoline, glyoxal benzothiazoline, biacetylbenzothiazoline, benzil benzothiazoline, and terphthaldehyde benzothiazoline have been described. The newly synthesized complexes, [MoO2(Bzt)2] and [MoO2(Bzt')] (where BztH and Bzt'H2 represent benzothazoline molecules) have been characterized by elemental analysis, conductance measurements, molecular weight determinations, and magnetic studies. Based on IR, 1H NMR, 13C NMR, and electronic spectral studies, distorted octahedral geometry with cis-MoO2 group has been indicated for the resulting complexes. Two benzothiazolines and their corresponding metal complexes were screened for their antifungicidal and antibacterial activity on several fungi and bacteria and found to be quite active in this respect. In addition, antifertility activity of representative ligands and their molybdenum complexes was also evaluated and discussed in male mice.

Resonance Raman studies of the flavin and iron-sulfur centers of milk xanthine oxidase

Resonance Raman spectroscopy has been used to study milk xanthine oxidase, an enzyme containing molybdenum, binuclear iron-sulfur clusters, and FAD as cofactors. The contribution of FAD dominates the resonance Raman spectrum at frequencies above 500 cm-1. As expected, no bands assignable to FAD are observed in deflavo xanthine oxidase. The resonance Raman spectrum below 500 cm-1 reveals the contribution of the Fe2S2(Cys)4 groups with frequencies similar to those of adrenodoxin and putidaredoxin. Resonance enhancement profiles of the Fe2S2(Cys)4 clusters indicate intensity variations among the Fe2S2(Cys)4 peaks that are attributed to different excitation wavelength maxima of their bridging and terminal iron-sulfur vibrations. No evidence for Mo-ligand vibrations could be obtained by using excitation wavelengths between 363.8 and 514.5 nm.

Activation of nit-1 nitrate reductase by W-formate dehydrogenase

Formate dehydrogenase ( FDH ) from Clostridium thermoaceticum is a known tungsten enzyme. FDH was tested for the presence of nitrogenase-type cofactor and nitrate reductase-type cofactor by the Azotobacter vinelandii UW-45 and Neurospora crassa nit-1 reconstitution assays, respectively. Tungsten formate dehydrogenase (W- FDH ), containing only a small Mo impurity, activated the nit-1 nitrate reductase extracts when molybdate was also added, but not when tungstate was added. These results show W- FDH contains the cofactor common to all known Mo-enzymes except nitrogenase. The difference between the redox chemistries of W- FDH and W-substituted sulfite oxidase appears to relate to differences in tungsten ligation other than that donated by the cofactor or to variations in the protein environment surrounding the tungsten active site.