Figure 2.

(A). The normalized equilibrium absorption spectra of ferric cytochrome P450_cam in 50 mM KPi buffer with 150 mM KCl at pH 7.4. The absorption band peaking at 417 nm is the camphor-free form and the spectrum peaking at 391 nm is the camphor-bound form. (B). Normalized femtosecond time-resolved optical transmittance of cytochrome P450_cam in the camphor-free (black) and camphor-bound (red) states. The excitation wavelength is 412 nm for camphor-bound (red) and 423 nm for camphor-free (black). The kinetic traces show a bleach followed by a recovery to equilibrium (ΔT > 0) and fitted with bi-exponential decay starting from 200 fs. The time constants (τ) and amplitudes (a) used as fitting parameters for the camphor free species are τ₁= 56 fs (a₁ = 0.79), τ₂= 1.5 ps (a₂ = 0.18) and offset = 0.02 and for camphor bound complex τ₁= 140 fs (a₁ = 0.36), τ₂= 1.1 ps (a₂ = 0.67) and offset = −0.03. The shortest time constant and its amplitude are distorted due to convolution with the coherence coupling signal.