TY - JOUR
T1 - Iso-mechanism of nitroalkane oxidase
T2 - 1. Inhibition studies and activation by imidazole
AU - Gadda, Giovanni
AU - Fitzpatrick, Paul F.
PY - 2000/2/15
Y1 - 2000/2/15
N2 - The flavoprotein nitroalkane oxidase catalyzes the oxidation of primary and secondary nitroalkanes to aldehydes and ketones, respectively, transferring electrons to oxygen to form hydrogen peroxide. The steady-state kinetic mechanism of the active flavin adenine dinucleotide-(FAD-) containing form of the enzyme has been determined with nitroethane at pH 7 to be bi-ter ping-pong, with oxygen reacting with the free reduced enzyme after release of the aldehyde product. The V(max) value is 5.5 ± 0.3 s-1 and the K(m) values for nitroethane and oxygen are 3.3 ± 0.6 and 0.023 ± 0.007 mM, respectively. The free reduced enzyme forms a dead-end complex with nitroethane, with a K(ai), value of 30 ± 6 mM. Acetaldehyde and butyraldehyde are noncompetitive inhibitors versus nitroethane due to formation of a dead-end complex between the oxidized enzyme and the product. Acetaldehyde is an uncompetitive inhibitor versus oxygen, indicating that an irreversible isomerization of the free reduced enzyme occurs before the reaction with oxygen. Addition of unprotonated imidazole results in a 5-fold increase in the V(max) value, while the V/K values for nitroethane and oxygen are unaffected. A 5-fold increase in the K(ai) value for nitroethane and a 6.5-fold increase in the K(ii) value for butyraldehyde are observed in the presence of imidazole. These results are consistent with the isomerization of the free reduced enzyme being about 80% rate-limiting for catalysis and with a model in which unprotonated imidazole accelerates the rate of isomerization.
AB - The flavoprotein nitroalkane oxidase catalyzes the oxidation of primary and secondary nitroalkanes to aldehydes and ketones, respectively, transferring electrons to oxygen to form hydrogen peroxide. The steady-state kinetic mechanism of the active flavin adenine dinucleotide-(FAD-) containing form of the enzyme has been determined with nitroethane at pH 7 to be bi-ter ping-pong, with oxygen reacting with the free reduced enzyme after release of the aldehyde product. The V(max) value is 5.5 ± 0.3 s-1 and the K(m) values for nitroethane and oxygen are 3.3 ± 0.6 and 0.023 ± 0.007 mM, respectively. The free reduced enzyme forms a dead-end complex with nitroethane, with a K(ai), value of 30 ± 6 mM. Acetaldehyde and butyraldehyde are noncompetitive inhibitors versus nitroethane due to formation of a dead-end complex between the oxidized enzyme and the product. Acetaldehyde is an uncompetitive inhibitor versus oxygen, indicating that an irreversible isomerization of the free reduced enzyme occurs before the reaction with oxygen. Addition of unprotonated imidazole results in a 5-fold increase in the V(max) value, while the V/K values for nitroethane and oxygen are unaffected. A 5-fold increase in the K(ai) value for nitroethane and a 6.5-fold increase in the K(ii) value for butyraldehyde are observed in the presence of imidazole. These results are consistent with the isomerization of the free reduced enzyme being about 80% rate-limiting for catalysis and with a model in which unprotonated imidazole accelerates the rate of isomerization.
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U2 - 10.1021/bi9922547
DO - 10.1021/bi9922547
M3 - Article
C2 - 10684620
AN - SCOPUS:0034673122
VL - 39
SP - 1400
EP - 1405
JO - Biochemistry
JF - Biochemistry
SN - 0006-2960
IS - 6
ER -