Oxygenase domain of Drosophila melanogaster nitric oxide synthase: unique kinetic parameters enable a more efficient NO release.
Although nitric oxide (NO) is important for cell signaling and nonspecific immunity in the fruit fly Drosophila melanogaster, little is known about its single NO synthase (dNOS). We expressed the oxygenase domain of dNOS (dNOSoxy), characterized its spectroscopic, kinetic, and catalytic properties, and interpreted them in light of a global kinetic model for NO synthesis. Single turnover reactions with ferrous dNOSoxy showed it could convert Arg to N'omega-hydroxy-l-arginine (NOHA), or NOHA to citrulline and NO, when it was given 6R-tetrahydrobiopterin and O2. The dNOSoxy catalyzed Arg hydroxylation and NOHA oxidation at rates that matched or exceeded the rates catalyzed by the three mammalian NOSoxy enzymes. Consecutive heme-dioxy, ferric heme-NO, and ferric heme species were observed in the NOHA reaction of dNOSoxy, indicating that its catalytic mechanism is the same as in the mammalian NOS. However, NO dissociation from dNOSoxy was 4 to 9 times faster than that from the mammalian NOS enzymes. In contrast, the dNOSoxy ferrous heme-NO complex was relatively unreactive toward O2 and in this way was equivalent to the mammalian neuronal NOS. Our data show that dNOSoxy has unique settings for the kinetic parameters that determine its NO synthesis. Computer simulations reveal that these unique settings should enable dNOS to be a more efficient and active NO synthase than the mammalian NOS enzymes, which may allow it to function more broadly in cell signaling and immune functions in the fruit fly.
Ray
Sougata Sinha
SS
Department of Biochemistry, University College of Sciences, Calcutta University, West Bengal 700 019, India.
Tejero
Jesús
J
Wang
Zhi-Qiang
ZQ
Dutta
Tanmay
T
Bhattacharjee
Arindam
A
Regulski
Michael
M
Tully
Tim
T
Ghosh
Sanjay
S
Stuehr
Dennis J
DJ
D000818:Animals; D001120:Arginine / Q000737:chemistry; D001708:Biopterins / Q000031:analogs & derivatives / Q000737:chemistry; D002021:Buffers; D002384:Catalysis; D003198:Computer Simulation; D004331:Drosophila melanogaster / Q000201:enzymology*; D004492:Edetic Acid / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics; D005296:Ferrous Compounds / Q000737:chemistry; D006418:Heme / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000737:chemistry*; D010084:Oxidation-Reduction; D010105:Oxygenases / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
D002021:Buffers; D005296:Ferrous Compounds; D001708:Biopterins; D009569:Nitric Oxide; D006418:Heme; D001120:Arginine; D004492:Edetic Acid; D010105:Oxygenases; D019001:Nitric Oxide Synthase; C003402:sapropterin