Journal of Bacteriology, February 2000, p. 789-795, Vol. 182, No. 3
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Departamento de Genética, Facultad de Biología, Universidad de Sevilla, 41080 Seville, Spain,1 and Chemische Mikrobiologie, Bergische Universität-Gesamthochschule Wuppertal, D-42097 Wuppertal, Germany2
Received 8 September 1999/Accepted 9 November 1999
A genomic region involved in tetralin biodegradation was recently
identified in Sphingomonas strain TFA. We have cloned and sequenced from this region a gene designated thnC, which
codes for an extradiol dioxygenase required for tetralin utilization. Comparison to similar sequences allowed us to define a subfamily of
1,2-dihydroxynaphthalene extradiol dioxygenases, which comprises two
clearly different groups, and to show that ThnC clusters within group 2 of this subfamily. 1,2-Dihydroxy-5,6,7,8-tetrahydronaphthalene was
found to be the metabolite accumulated by a thnC insertion mutant. The ring cleavage product of this metabolite exhibited behavior
typical of a hydroxymuconic semialdehyde toward pH-dependent changes
and derivatization with ammonium to give a quinoline derivative. The
gene product has been purified, and its biochemical properties have
been studied. The enzyme is a decamer which requires Fe(II) for
activity and shows high activity toward its substrate
(Vmax, 40.5 U mg
1;
Km, 18.6 µM). The enzyme shows even higher
activity with 1,2-dihydroxynaphthalene and also significant activity
toward 1,2-dihydroxybiphenyl or methylated catechols. The broad
substrate specificity of ThnC is consistent with that exhibited by
other extradiol dioxygenases of the same group within the subfamily of
1,2-dihydroxynaphthalene dioxygenases.
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