A synthetic growth medium was
purified
with the chelator 1,5-diphenylthiocar-bazone to study the effects of
copper
on partial reactions and product formation of nitrite respiration in Pseudomonas
perfectomarinus. This organism grew anaerobically in a
copper-deficient
medium with nitrate or nitrite as the terminal electron acceptor.
Copper-deficient
cells had high activity for reduction of nitrate, nitrite, and nitric
oxide,
but little activity for nitrous oxide reduction. High rates of nitrous
oxide reduction were observed only in cells grown on a
copper-sufficient
(1 µM) medium. Copper-deficient cells converted nitrate or
nitrite
initially to nitrous oxide instead of dinitrogen, the normal end
product
of nitrite respiration in this organism. In agreement with this was the
finding that anaerobic growth of P. perfectomarinus with
nitrous
oxide as the terminal electron acceptor required copper. This
requirement
was not satisfied by substitution of molybdenum, zinc, nickel, cobalt,
or manganese for copper. Reconstitution of nitrous oxide reduction in
copper-deficient
cells was rapid on addition of a small amount of copper, even though
protein
synthesis was inhibited. The results indicate an involvement of copper
protein(s) in the last step of nitrite respiration in P.
perfectomarinus.
In addition we found that nitric oxide, a presumed intermediate of
nitrite
respiration, inhibited nitrous oxide reduction.