NO reductase synthesis was
investigated
immunochemically and by activity assays in cells of Pseudomonas
stutzeri
ZoBell grown in continuous culture at discrete aeration levels, or in O2-limited
batch cultures supplemented with N oxides as respiratory substrate.
Under
aerobic conditions, NO reductase was not expressed in P. stutzeri.
Oxygen limitation in combination with the presence of nitrate or
nitrite
derepressed NO reductase synthesis. On transition from aerobic to
anaerobic
conditions in continuous culture, NO reductase was synthesized below 3%
air saturation and reached maximum expression under anaerobic
conditions.
By use of mutant strains defective in nitrate respiration or nitrite
respiration,
the inducing effect of individual N oxides on NO reductase synthesis
could
be discriminated. Nitrite caused definite, concentration-dependent
induction,
while nitrate promoted moderate enzyme synthesis or amplified effects
of
nitrite. Exogenous nitric oxide (NO) in concentrations £
25
µM induced trace amounts of NO reductase; in higher
concentrations
it arrested cell growth. Nitrite reductase or NO reductase were not
detected
immunochemically under these conditions. NO generated as an
intermediate
appeared not to induce NO reductase significantly. Antiserum raised
against
the P. stutzeri NO reductase showed crossreaction with cell
extracts
from P. stutzeri JM300, but not with several other denitrifying
pseudomonads or Paracoccus denitrificans.