Mechanism of nitrogenase switch-off by oxygen. [Klebsiella pneumoniae; Rhodopseudomonas sphaeroides f. sp. denitrificans; Rhodopseudomonas capsulate]
Oxygen caused a reversible inhibition (switch-off) of nitrogenase activity in whole cells of four strains of diazotrophs, the facultative anaerobe Klebsiella pneumoniae and three strains of photosynthetic bacteria (Rhodopseudomonas sphaeroides f. sp. denitrificans and Rhodopseudomonas capsulata strians AD2 and BK5). In K. pneumoniae 50% inhibition of acetylene reduction was attained at an O/sub 2/ concentration of 0.37 ..mu..M. Cyanide (90 ..mu..M), which did not affect acetylene reduction but inhibited whole-cell respiration by 60 to 70%, shifted the O/sub 2/ concentration that caused 50% inhibition of nitrogenase activity to 2.9 ..mu..M. A mutant strain of K. pneumoniae, strain AH11, has a respiration rate that is 65 to 75% higher than that of the wild type, but is nitrogenase activity is similar to wild-type activity. Acetylene reduction by whole cells of this mutant was inhibited 50% by 0.20 ..mu..M O/sub 2/. Inhibition by CN/sup -/ of 40 to 50% of the O/sub 2/ uptake in the mutant shifted the O/sub 2/ concentration that caused 50% inhibition of nitrogenase to 1.58 ..mu..M. Thus, when the respiration rates were lower, higher oxygen concentrations were required to inhibit nitrogenase. Reversible inhibition of nitrogenase activity in vivo was caused under anaerobic conditions by other electron acceptors. Addition of 2 mM sulfite to cell suspensions of R. capsulata B10 and R. sphaeroides inhibited nitrogenase activity. Nitrite also inhibited acetylene reduction in whole cells of the photodenitrifier R. sphaeroides but not in R. capsulata B10, which is not capable of enzymatic reduction of NO/sub 2//sup -/. Lower concentrations of NO/sub 2//sup -/ were required to inhibit the activity in NO/sub 3//sup -/-grown cells, which have higher activities of nitrite reductase.
- Research Organization:
- Tel-Aviv Univ., Israel
- OSTI ID:
- 6407019
- Journal Information:
- J. Bacteriol.; (United States), Vol. 169:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
KLEBSIELLA
ENZYME ACTIVITY
NITROGENASE
OXYGEN
BIOLOGICAL EFFECTS
RHODOPSEUDOMONAS
INHIBITION
NITRITES
NITROGEN FIXATION
RESPIRATION
SULFITES
BACTERIA
ELEMENTS
ENZYMES
MICROORGANISMS
NITRO-GROUP DEHYDROGENASES
NITROGEN COMPOUNDS
NONMETALS
OXIDOREDUCTASES
OXYGEN COMPOUNDS
SULFUR COMPOUNDS
560300* - Chemicals Metabolism & Toxicology