FIGURE 1.

Time-dependent optical spectral changes of α₁β₁-NO complex formation. 4 μm sGC prepared anaerobically as described under “Experimental Procedures” was mixed with an equal volume of anaerobic 50 mm TEA buffer (pH 7.4) without (A–D) or with (E) 2 mm Mg²⁺-GTP, incubated for 100 ms in the aging loop of the stopped-flow instrument, and mixed with equimolar (A–C and E) or 5-fold excess (D) NO. Spectra were recorded for different time intervals (1 s (A), 32 s (B), and 262 s (C–E)) at a rate of 400 spectra per time interval. Spectra for the initial sGC (dashed lines) were obtained in separate measurements in which NO solution was replaced with 50 mm TEA buffer (pH 7.4). The base line for all spectra was adjusted based on the 700 nm value. Representative spectra out of at least four independent experiments with different sGC preparations are shown. AU, absorbance unit.