Picosecond Infrared Spectroscopy in Heme Proteins

Many aspects of the protein dynamics involved in ligand binding to heme proteins remain poorly understood. Infrared (IR) vibrational spectroscopy is particularly useful in studying behavior of the ligand since other optical spectroscopies tend to focus on the chromophores in the protein. Matrix isolation IR experiments establish the existence of metastable intermediates below 200K after photodissociation of ligated myoglobin. We report analogous time-resolved experiments with 0.5 ps resolution on carboxyhemoglobin (HbCO) in water at 300K. A seeded optical parametric amplifier is used to generate tunable 300 fs probe pulses in the mid-IR which monitor the evolution of the CO stretching vibration during photodissociation of the HbCO by 300 fs pulses of 585 nm radiation.