The goal of the proposed research is to elucidate molecular and physical determinants important for the catalytic efficiency and regulation of the enzyme, assimilatory NADH:nitrate reductase. This enzyme catalyzes the rate-limiting and regulated step in the process of nitrate assimilation which is the major pathway by which inorganic nitrogen is converted to a biologically usable form in eukaryotes and a variety of macroorganisms. Nitrate reductase is a multimeric enzyme which contains FAD, heme and molybdopterin prosthetic groups and transfers electron from NADH to nitrate. In addition to its biological importance, this enzyme represents and excellent model for investigating electron transfer reactions in complex proteins and shares several common mechanistic and structural features with other molybdo-, heme-, or flavo-enzymes. The specific objectives of the proposed research are to correlate the thermodynamic parameters and kinetic properties of the enzyme under various environmental conditions which relate to physiological functions. These conditions include pH, substrates, products, and known effectors such as phosphate and cyanide. Thermodynamic parameters and properties of individual prosthetic groups, identification and properties of important functional groups and kinetic parameters for individual steps will be determined by a combination of UV/vis, room temperature epr and CD spectroscopies; microcoulometry; stopped flow, freeze-quench epr and laser flash photolysis; and chemical methods. Conserved properties will be determined by selective comparative studies of nitrate reductases from various sources. Studies utilizing various substituted forms of nitrate reductase (FAD analogues, W and selenomethionine substituted forms) and limited proteolytic products will allow dissection and study of functional domains of the enzyme.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM032696-06
Application #
3281748
Study Section
Physical Biochemistry Study Section (PB)
Project Start
1984-09-27
Project End
1992-03-31
Budget Start
1990-04-01
Budget End
1991-03-31
Support Year
6
Fiscal Year
1990
Total Cost
Indirect Cost
Name
University of South Florida
Department
Type
Schools of Medicine
DUNS #
City
Tampa
State
FL
Country
United States
Zip Code
33612
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Percy, M J; Crowley, L J; Roper, D et al. (2006) Identification and characterization of the novel FAD-binding lobe G75S mutation in cytochrome b(5) reductase: an aid to determine recessive congenital methemoglobinemia status in an infant. Blood Cells Mol Dis 36:81-90
Roma, Glenn W; Crowley, Louis J; Barber, Michael J (2006) Expression and characterization of a functional canine variant of cytochrome b5 reductase. Arch Biochem Biophys 452:69-82
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Davis, C Ainsley; Barber, Michael J (2004) Cytochrome b5 oxidoreductase: expression and characterization of the original familial ideopathic methemoglobinemia mutations E255- and G291D. Arch Biochem Biophys 425:123-32
Davis, C Ainsley; Crowley, Louis J; Barber, Michael J (2004) Cytochrome b5 reductase: the roles of the recessive congenital methemoglobinemia mutants P144L, L148P, and R159*. Arch Biochem Biophys 431:233-44
Pollock, Veronica V; Conover, Richard C; Johnson, Michael K et al. (2003) Biotin sulfoxide reductase: Tryptophan 90 is required for efficient substrate utilization. Arch Biochem Biophys 409:315-26
Bewley, Maria C; Davis, C Ainsley; Marohnic, Christopher C et al. (2003) The structure of the S127P mutant of cytochrome b5 reductase that causes methemoglobinemia shows the AMP moiety of the flavin occupying the substrate binding site. Biochemistry 42:13145-51

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