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J. Bacteriol., 01 1995, 378-384, Vol 177, No. 2
NJ Brown-Peterson and ML Salin
When subjected to the stress of growth in a relatively low-salt environment
(1.25 M NaCl), the halophilic bacterium Halobacterium halobium induces a
catalase. The protein has been purified to electrophoretic homogeneity and
has an M(r) of 240,000 and a subunit size of approximately 62,000. The
enzyme is active over a broad pH range of 6.5 to 10.0, with a peak in
activity at pH 7.0. It has an isoelectric point of 4.0. This catalse, which
is not readily reduced by dithionite, shows a Soret peak at 406 nm. Cyanide
and azide inhibit the enzyme at micromolar concentrations, whereas
maleimide is without effect. The addition of 20 mM 3-amino-1,2,4-triazole
results in a 33% inhibition in enzymatic activity. The tetrameric protein
binds NADP in a 1:1 ratio but does not peroxidize NADPH, NADH, or
ascorbate. Although the enzymatic activity is maximal when assayed in a 50
mM potassium phosphate buffer with no NaCl, prolonged incubation in a
buffer lacking NaCl results in inactive enzyme. Moreover, purification must
be performed in the presence of 2 M NaCl. Equally as effective in retaining
enzymatic function are NaCl, LiCl, KCl, CsCl, and NH4Cl, whereas divalent
salts such as MgCl2 and CaCl2 result in the immediate loss of activity. The
catalase is stained by pararosaniline, which is indicative of a glycosidic
linkage. The Km for H2O2 is 60 mM, with inhibition observed at
concentrations in excess of 90 mM. Thus, the mesohalic catalase purified
from H. halobium seems to be similar to other catalases, except for the
salt requirements, but differs markedly from the constitutive halobacterial
hydroperoxidase.
Copyright © 1995, American Society for Microbiology
Purification and characterization of a mesohalic catalase from the halophilic bacterium Halobacterium halobium
Department of Biochemistry and Molecular Biology, Mississippi State University, Mississippi 39762.
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