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J. Bacteriol., Jun 1995, 3111-3119, Vol 177, No. 11
ER Rocha and CJ Smith
A single catalase enzyme was produced by the anaerobic bacterium
Bacteroides fragilis when cultures at late log phase were shifted to
aerobic conditions. In anaerobic conditions, catalase activity was detected
in stationary-phase cultures, indicating that not only oxygen exposure but
also starvation may affect the production of this antioxidant enzyme. The
purified enzyme showed a peroxidatic activity when pyrogallol was used as
an electron donor. It is a hemoprotein containing one heme molecule per
holomer and has an estimated molecular weight of 124,000 to 130,000. The
catalase gene was cloned by screening a B. fragilis library for
complementation of catalase activity in an Escherichia coli catalase mutant
(katE katG) strain. The cloned gene, designated katB, encoded a catalase
enzyme with electrophoretic mobility identical to that of the purified
protein from the B. fragilis parental strain. The nucleotide sequence of
katB revealed a 1,461-bp open reading frame for a protein with 486 amino
acids and a predicted molecular weight of 55,905. This result was very
close to the 60,000 Da determined by denaturing sodium dodecyl
sulfate-polyacrylamide gel electrophoresis of the purified catalase and
indicates that the native enzyme is composed of two identical subunits. The
N-terminal amino acid sequence of the purified catalase obtained by Edman
degradation confirmed that it is a product of katB. The amino acid sequence
of KatB showed high similarity to Haemophilus influenzae HktE (71.6%
identity, 66% nucleotide identity), as well as to gram-positive bacterial
and mammalian catalases. No similarities to bacterial catalase-peroxidase-
type enzymes were found.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Biochemical and genetic analyses of a catalase from the anaerobic bacterium Bacteroides fragilis
Department of Microbiology and Immunology, School of Medicine, East Carolina State University, Greenville, North Carolina 27858-4354, USA.
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