Yasuhisa MIZUTANI and Teizo KITAGAWA
[Science 278, 443 (1997)]
The formation of vibrationally excited heme upon photodissociation of carbonmonoxy-myoglobin and its subsequent vibrational energy relaxation was monitored by picosecond anti-Stokes resonance Raman spectroscopy. The anti-Stokes intensity of the (nu)4 band showed immediate generation of vibrationally excited hemes and biphasic decay of the excited populations. The best fit to double exponentials gave time constants of 1.9 ± 0.6 and 16 ± 9 ps for vibrational population decay and 3.0 ± 1.0 and 25 ± 14 ps for temperature relaxation of the photolyzed heme when a Boltzmann distribution is assumed. The decay of the (nu)4 anti-Stokes intensity is accompanied by narrowing and frequency-upshift of the Stokes counterpart. These are the first direct monitoring of cooling dynamics of the heme cofactor within a globin matrix which would lead to characterization of how vibrational energy flows through the protein moiety and to the water bath.