Figure 2
The inhibitory effect of cd1NiR on cNOR catalysis. (a) NO reduction profile of P. denitrificans cNOR in the absence (black line) and presence (red line) of cd1NiR. Experimental conditions: 50 mM HEPES pH 7.0, 50 mM KCl, 0.05% DDM, 30 mM glucose, 1 U/ml glucose oxidase, 20 U/ml catalase. Once the chamber was anaerobic, cyt. c (15 µM), TMPD (0.5 mM), and 5 times 10 µM NO (from NO-saturated water) was added. At t ~250 s, ascorbate (3 mM) and cNOR (80 nM) were added. For the trace with cd1NiR (80 nM), it was added before the addition of NO. (b) Titration of the inhibitory effect of cd1NiR on cNOR catalysis. Experimental conditions as in A, except the cNOR concentration was 40 nM, and the cd1NiR concentration varied between 0–200 nM. cNOR activity (black circles) refers to the kmax at ~5 µM NO, with the kmax in the absence of cd1NiR set at 100%. Also shown is the effect of adding cd1NiR on substrate inhibition (blue circles) for NO-reduction by cNOR. The right y-axis refers to the [NO] where kmax/2 is reached (termed Kiapp in the text, note that this is higher than for kmax).
