Figure 1.

NO reductase activity of ba₃ and caa₃. (Upper) ba₃ (1.5 μM) was degassed, reduced by 10 mM ascorbate, 100 μM TMPD, 1 μM cytochrome c₅₅₂, and, after addition of 60 μM NO, mixed in the stopped flow with 104 μM deoxy-Hb at the following incubation times: 0.9, 1.8, 3.4, 7.5, 10.8, 16, and 26.8 min. Difference spectra, collected at 100 ms after mixing, show NO disappearing from solution. Baseline, deoxy-Hb in the presence of ba₃ and reductants before addition of NO; dashed spectrum, 104 μM NO-saturated Hb. (Lower) NO consumption as a function of time after addition of NO (60 μM final concentration) to: 10 mM ascorbate + 200 μM ruthenium hexamine (●) or 10 mM ascorbate + 10 μM TMPD (*); 5 μM (aa₃) beef heart oxidase reduced by 10 mM ascorbate and 200 μM ruthenium hexamine (○); 1.5 μM ba₃ reduced by 10 mM ascorbate + 200 μM ruthenium hexamine (□) or by 10 mM ascorbate + 10 μM TMPD + 1 μM cytochrome c₅₅₂ (■); 0.3 μM caa₃ reduced by 10 mM ascorbate and 10 μM TMPD (▴); or 100 μM TMPD (▵). Contrary to beef heart oxidase, both oxidases from T. thermophilus catalyze NO consumption significantly faster than reductants alone.