FIGURE 2.

Heme dissociates from the wild-type NC1 slowly, and P351A increases the rate. Heme-bound NC1, either P351A (A and B) or wild-type (C), was incubated with a 6-fold excess of apomyoglobin at 25 °C. A, electronic absorption spectra obtained at 0, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, and 90 min. B, the 414-nm (metmyoglobin) and 447-nm (P351A-heme complex) values shown in A were fit to a single exponential function. The rates shown are mean ± S.D. of three independent repeats. C, wild-type NC1 showed no significant changes of absorbance at 414 nm and 450 nm at room temperature over 4 days.