Figure 4.

Oxidation of hIYD·fl_hq by O₂. A solution containing hIYD·fl_hq (5 μM final) in 500 mM NaCl, 10% glycerol, 1 mM DTT, and 50 mM sodium phosphate, pH 7.4, was mixed with an equal volume of an oxygenated solution containing 500 mM NaCl, 10% glycerol, 1 mM DTT, and 50 mM sodium phosphate, pH 7.4. (A) Spectra of hIYD·fl_hq oxidation by air-saturated buffer were recorded from 4 ms to 7 s with a diode array spectrophotometer. The arrow indicates the direction of spectral change as a function of time. (B) Oxidation of hIYD·fl_hq was monitored by absorbance at 446 nm, and the resulting k_obs values (see Figure S3) were plotted against oxygen concentration to determine the second-order rate constant (k_ox). Data points represent the average of three independent measurements, and the standard deviations are illustrated by error bars. The solid line was generated by a linear best fit to the data.