Hydrogen-mediated enhancement of hydrogenase expression in Azotobacter vinelandii.
Azotobacter vinelandii cultures express more H2 uptake hydrogenase activity when fixing N2 than when provided with fixed N. Hydrogen, a product of the nitrogenase reaction, is at least partly responsible for this increase. The addition of H2 to NH4+-grown wild-type cultures caused increased whole-cell H2 uptake activity, methylene blue-dependent H2 uptake activity of membranes, and accumulation of hydrogenase protein (large subunit as detected immunologically) in membranes. Both rifampin and chloramphenicol inhibited the H2-mediated enhancement of hydrogenase synthesis. Nif- A. vinelandii mutants with deletions or insertions in the nif genes responded to added H2 by increasing the amount of both whole-cell and membrane-bound hydrogenase activities. Nif- mutant strain CA11 contained fourfold more hydrogenase protein when incubated in N-free medium with H2 than when incubated in the same medium containing Ar. N2-fixing wild-type cultures that produce H2 did not increase hydrogenase protein levels in response to added H2.
Prosser
J
J
Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218.
Graham
L
L
Maier
R J
RJ
D001395:Azotobacter / Q000201:enzymology* / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism*; D006864:Hydrogenase / Q000096:biosynthesis*; D009586:Nitrogen Fixation
D006859:Hydrogen; D006864:Hydrogenase