Long-lived amide I vibrational modes in myoglobin

Pump-probe experiments in the infrared measure vibrational relaxation rates . Myoglobin, which is almost entirely alpha helix in secondary structure, h as an unusually long, nonexponential excited state relaxation generated by optically pumping at the blue side (5.85 mu m) of the amide I band. The ami no acid alanine and the predominantly beta sheet protein photoactive yellow protein do not have such a long-lived state, suggesting that the alpha hel ix in proteins can support nonlinear states of 15 ps characteristic times.