Probing the nonoxidative tautomerization of nitroethane to ethylnitronate catalyzed by 2-nItropropane dioxygenase with pH and substrate kinetic isotope effects

BIOL 74

Kevin Francis, kev8796@yahoo.com, Department of Chemistry, Georgia State University, PO BOX 4098, Atlanta, GA 30302-4098 and Giovanni Gadda, Depatment of Chemistry, Georgia State University, 50 Decatur street, Atlanta, GA 30303.
2-Nitropropane dioxygenase is an FMN dependent enzyme that utilizes nitroalkanes as substrate in either their neutral or anionic (nitronate) form. Previous mechanistic studies are consistent with substrate oxidation occurring through the formation of an anionic flavosemiquinone intermediate. A recent study of the pH dependence of the alfa-secondary kinetic isotope effect with on the kcat/Km value with 1-[2H]-ethylnitronate demonstrated that the enzyme also catalyzes the non-oxidative tautomerization of ethylnitronate to nitroethane. The present study demonstrates that a similar nitro-aci tautomerization occurs with nitroethane, in which the neutral substrate is deprotonated to form ethylnitronate without involvement of the flavin cofactor. The pH dependence of the kinetic isotope effects with 1,1-[2H2]-nitroethane as substrate for the enzyme was studied under steady-state conditions. The mechanistic implications of both the enzymatic and non-enzymatic deprotonation of nitroethane are discussed. This study was supported by PRF Grant (# 47363-AC4) from the ACS.

 

Frontiers in Chemical Biology
5:00 PM-7:00 PM, Sunday, August 19, 2007 BCEC -- Exhibit Hall - B2, Poster

Division of Biological Chemistry

The 234th ACS National Meeting, Boston, MA, August 19-23, 2007