The nitrogenase activity of the microaerophilic bacteria Azospirillum brasilense and A. lipoferum was completely inhibited by 2.0 kPa of oxygen (approximately 0.02 atm of O2) in equilibrium with the solution. The activity could be partially recovered at optimal oxygen concentrations of 0.2 kPa. In contrast to the NH4+ switch off, no covalent modification of the nitrogenase reductase (Fe protein...

In the modern ocean, a significant amount of nitrogen fixation is attributed to filamentous, nonheterocystous cyanobacteria of the genus Trichodesmium. In these organisms, nitrogen fixation is confined to the photoperiod and occurs simultaneously with oxygenic photosynthesis. Nitrogenase, the enzyme responsible for biological N2 fixation, is irreversibly inhibited by oxygen in vitro. How nitrog...

Nitrite was able to strongly inhibit C(2)H(2) reduction by nitrogenase from soybean bacteroids, whereas H(2) evolution was unaffected under the same conditions. NO inhibited both C(2)H(2) reduction and H(2) evolution; during C(2)H(2) reduction, sensitivity of nitrogenase to NO was higher than to NO(2), and the K(i) values were, respectively, 0.056 and 0.52 mM. Production of NO resulting from a ...

An intact method for measuring immediately linear rates of acetylene reduction was used to investigate the relationship between temperature, pH, O(2) concentration, and light intensity with the rate of root-associated nitrogenase activity in rice (Oryza sativa L.). Nitrogenase activity varied over a temperature range of 10 to 50 degrees C and optimal rates of acetylene reduction were recorded a...

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 strains AD2 and BK5). In K. pneumoniae 50% inhibition of acetylene reduction was attained at an O2 co...

In a small-scale reaction, vanadium-dependent nitrogenase has previously been shown to catalyze reductive catenation of carbon monoxide (CO) to ethylene, ethane, propylene, and propane. Here, we report the identification of additional hydrocarbon products [α-butylene, n-butane, and methane (CH(4))] in a scaled-up reaction featuring 20 milligrams of vanadium-iron protein, the catalytic component...

During the enzymic reduction of N2 to NH3 by Mo-nitrogenase, free hydrazine (N2H4) is not detectable, but an enzyme-bound intermediate can be made to yield N2H4 by quenching the enzyme during turnover [Thorneley, Eady & Lowe (1978) Nature (London) 272, 557-558]. In contrast, we show here that the V-nitrogenase of Azotobacter chroococcum produces a small but significant amount of free N2H4 (up t...

Activating enzyme (AE) is responsible for the in vitro activation of inactive Fe protein of nitrogenase from Rhodospirillum rubrum cells cultured anaerobically with glutamate as the N source. The expression of Fe protein and AE was examined in R. rubrum cultured photosynthetically or aerobically on media containing malate as the carbon source. One of the following N sources was used in each cul...

Phototrophic continuous and batch cultures of Rhodobacter capsulatus were employed to identify the C/N ratio above which nitrogenase is de-repressed. The cultures were grown with limiting am ounts of am m onium as source of bound nitrogen and with L-lactate or lm alate as sources of carbon and reducing equivalents. De-repression of nitrogenase was determ ined on the basis of the occurrence of d...

During the process of biological nitrogen fixation, the enzyme nitrogenase catalyzes the ATP-dependent reduction of dinitrogen to ammonia. Nitrogenase consists of two component metalloproteins, the iron (Fe) protein and the molybdenum-iron (MoFe) protein; the Fe protein mediates the coupling of ATP hydrolysis to interprotein electron transfer, whereas the active site of the MoFe protein contain...