Structures of photolyzed carboxymyoglobin

Area of Science:

• Biophysics
• Spectroscopy
• Protein dynamics

Background:

• Carboxymyoglobin (MbCO) is a crucial protein for oxygen transport.
• Understanding the structural and electronic states of MbCO is vital for elucidating its function.
• Photoactivation of MbCO (Mb*CO) leads to transient structural changes.

Purpose of the Study:

• To investigate the structural and electronic properties of photoactivated carboxymyoglobin (Mb*CO) at low temperatures.
• To compare the states of Mb*CO with ground-state MbCO and deoxy-myoglobin (deoxy-Mb).
• To elucidate the perturbation of carbon monoxide (CO) upon photoactivation.

Main Methods:

• Fourier transform infrared (FT-IR) spectroscopy
• Visible spectroscopy
• Near-infrared spectroscopy
• Comparison with existing Mössbauer and magnetic susceptibility data

Main Results:

• FT-IR identified two energy states for CO in Mb*CO, significantly shifted from free CO gas.
• Mb*CO exhibits near-infrared absorption near 766 nm, similar to deoxy-Mb (758 nm).
• Iron in both Mb*CO and deoxy-Mb is confirmed to be in the high-spin Fe(II) state.

Conclusions:

• The electronic structure of iron in Mb*CO is nearly identical to that of deoxy-Mb.
• The carbon monoxide ligand in Mb*CO is only slightly perturbed from its state in free gas.
• Photoactivation induces distinct CO energy states within the myoglobin structure.