Catalases are key antioxidant enzymes in aerobic organisms.
Myxococcus xanthus expresses two monofunctional catalases,
small-subunit Cat1 and large-subunit Cat2. The Km of
H2O2 for recombinant Cat1 and Cat2 were 14.0 and 9.0 mM,
respectively, and the catalytic efficiency of Cat2 (kcat/Km =
500 sec-1 mM-1) was 4-fold higher than that of Cat1. The activity
ratio of Cat1 to Cat2 in the exponential growth phase
of M. xanthus was 1 to 3–4. A Cat1-deficient strain was constructed,
whereas a Cat2-deficient strain could not be produced.
In H2O2-supplemented medium, the cat1 mutant exhibited
marked growth retardation and a longer generation
time than the wild-type (wt) strain. After 2 h of incubation
in 0.5 mM H2O2-supplemented medium, the catalase activity
of the wt strain significantly increased (by 64-fold), but that
of the cat1 mutant strain did not. Under starvation-induced
developmental conditions, catalase activity was induced by
approximately 200-fold in both wt and cat1 strains, although
in the mutant the activity increase as well as spore formation
occurred one day later, indicating that the induction of catalase
activity during starvation was due to Cat2. In wt starved
cells, catalase activity was not induced by H2O2. These results
suggest that Cat2 is the primary housekeeping catalase
during M. xanthus growth and starvation-induced development,
whereas Cat1 may have a complementary role, being
responsible for the rapid degradation of H2O2 in proliferating
vegetative cells subjected to oxidative stress.
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