9419019 Johnson The objective of this research is to investigate the structural and functional diversity of Mo-pterin and W-pterin centers in terms of Mo/W coordination environment and the nature and properties of the molybdopterin component. The approach involves the use of three complementary spectroscopic techniques that are capable of selectively monitoring the electronic, magnetic and vibrational properties of the Mo/W-pterin centers even in the presence of additional paramagnetic or chromophoric prosthetic groups. Ground and excited state electronic properties for Mo(V) and W(V) forms will be established by variable temperature magnetic circular dichroism and electron paramagnetic resonance spectroscopies. Vibrational frequencies for Mo/W-ligand and molybdopterin stretching modes will be investigated by resonance Raman spectroscopy using excitation into visible charge transfer bands/ Electronic and vibrational assignments will be based on resonance excitation profiles, isotope shifts, and studies of appropriate Mo/W model complexes. Spectroscopic studies will focus on five distinct classes of oxotransferases: hepatic sulfite oxidase, DMSO reductase from Rhodobacter sphaeroides, formate dehydrogenase from Clostridium thermoaceticum, aldehyde ferredoxin oxidoreductases from the hyperthermophilic archaea Pyrococcus furiosus and ES-4, formaldehyde ferredoxin oxidoreductases from the hyperthermophilic archaea Pyrococcus furiosus and Thermococcus litoralis. %%% Oxotransferases catalyze a diverse array of oxygen insertion/removal reactions that are of crucial importance in the metabolism of carbon, nitrogen and sulfur. In mesophilic organisms that function at ambient temperatures (plants, bacteria and mammals), many of these reactions are catalyzed by enzymes with a novel molybdopterin active site of unknown structure. Recent studies of hyperthermorphilic archaea from deep sea volcanic vents have revealed the presence of similar enzymes with tungstopteri n active sites, that appear to be evolutionary ancestors of the mesophilic enzymes. The objective of this research is to investigate the structural and functional diversity of molybdopterin and tungstopterin oxotransferases in terms of molybdenum/tungsten coordination environment and the nature and properties of the pterin component. The approach involves the use of three complementary spectroscopic techniques that are capable of selectively monitoring the electronic, magnetic and vibrational properties of the molybdopterin and tungstopterin cofactors. Ground and excited state electronic properties for molybdenum(V) and tungsten(V) forms will be established by variable temperature magnetic circular dichroism and electron paramagnetic resonance spectroscopies. Vibrational frequencies for metal-ligand and pterin stretching modes will be investigated by resonance Raman spectroscopy using excitation into visible charge transfer bands. Electronic and vibrational assignments will be based on resonance excitation profiles, isotope shifts, and studies of appropriate molybdenum and tungsten model complexes. The results will be important in understanding the catalytic mechanisms of this class of enzymes and are likely to have important evolutionary and biotechnological implications. ***
