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Applied and Environmental Microbiology, March 1999, p. 946-950, Vol. 65, No. 3
Department of
Microbiology1 and Department of
Biochemistry,2 National University of
Singapore, 119260 Singapore
Received 29 June 1998/Accepted 7 December 1998
Two 3-hydroxybenzoate-inducible gentisate 1,2-dioxygenases were
purified to homogeneity from Pseudomonas alcaligenes NCIB 9867 (P25X) and Pseudomonas putida NCIB 9869 (P35X),
respectively. The estimated molecular mass of the purified
P25X gentisate 1,2-dioxygenase was 154 kDa, with a subunit mass of 39 kDa. Its structure is deduced to be a tetramer. The pI of
this enzyme was established to be 4.8 to 5.0. The subunit mass of P35X
gentisate 1,2-dioxygenase was 41 kDa, and this enzyme was deduced to
exist as a dimer, with a native molecular mass of
about 82 kDa. The pI of P35X gentisate 1,2-dioxygenase was around 4.6 to 4.8. Both of the gentisate 1,2-dioxygenases exhibited typical
saturation kinetics and had apparent Kms of 92 and 143 µM for gentisate, respectively. Broad substrate specificities were exhibited towards alkyl and halogenated gentisate analogs. Both
enzymes had similar kinetic turnover characteristics for gentisate,
with kcat/Km values of
44.08 × 104 s
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Purification and Characterization of Gentisate
1,2-Dioxygenases from Pseudomonas alcaligenes NCIB 9867 and Pseudomonas putida NCIB 9869
1 M
1 for the
P25X enzyme and 39.34 × 104 s
1
M
1 for the P35X enzyme. Higher
kcat/Km values
were expressed by both enzymes against the substituted
gentisates. Significant differences were observed between the
N-terminal sequences of the first 23 amino acid residues of the P25X
and P35X gentisate 1,2-dioxygenases. The P25X gentisate 1,2-dioxygenase
was stable between pH 5.0 and 7.5, with the optimal pH around 8.0. The
P35X enzyme showed a pH stability range between 7.0 and 9.0, and the
optimum pH was also 8.0. The optimal temperature for both P25X and P35X
gentisate 1,2-dioxygenases was around 50°C, but the P35X enzyme was
more heat stable than that from P25X. Both enzymes were strongly
stimulated by 0.1 mM Fe2+ but were
completely inhibited by the presence of 5 mM
Cu2+. Partial inhibition of both enzymes was also observed
with 5 mM Mn2+, Zn2+, and EDTA.
*
Corresponding author. Mailing address: Department of
Microbiology, Faculty of Medicine, National University of Singapore, 10 Kent Ridge Crescent, 119260 Singapore. Phone: 65-8743674. Fax: 65-7766872. E-mail: micpohcl{at}nus.edu.sg.
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