Fig 4.

NifZ activity is enhanced by sulfur acceptor ThiI in nonreducing conditions. Alanine formation monitored over time upon incubation with NifZ (0.01 mg, 0.3 μM) in the absence (▲) or presence of 6 μM ThiI (■). (Left) The linear rate of alanine formation under reducing (2 mM DTT) conditions shows activity levels of 354 ± 12 nmol/min/mg (solid line, NifZ) and 262 ± 24 nmol/min/mg (dashed line, NifZ + ThiI). (Right) NifZ activity under nonreducing conditions shows a linear rate of alanine formation (80 ± 1.4 nmol/min/mg), while in the presence of ThiI, displays a biphasic reaction profile for alanine production. The reaction velocity associated with the first phase of the reaction (250 ± 9.0 nmol/min/mg) was faster than the rate calculated for the second phase of the reaction (84 ± 5.5 nmol/min/mg). The graphs show representative curves from individual experiments. The velocities were calculated from a linear fit of alanine formation over time for each reaction or distinct phase within each reaction. The specific activities indicated above are the average of at least three independent experiments.