13C-NMR study of labeled vinyl groups in paramagnetic myoglobin derivatives.

Area of Science:

• Biophysical Chemistry
• Protein NMR Spectroscopy
• Bioinorganic Chemistry

Background:

• Myoglobin is a crucial protein for oxygen transport and storage.
• Understanding the electronic and structural properties of myoglobin is vital for deciphering its function.
• Nuclear magnetic resonance (NMR) spectroscopy offers powerful tools for probing molecular structure and dynamics.

Purpose of the Study:

• To assign and analyze carbon-13 (13C) NMR signals from vinyl groups in various sperm whale myoglobin derivatives.
• To investigate the electronic structure and bonding characteristics of myoglobin through hyperfine shifts.
• To compare the NMR spectral features of myoglobin with related model complexes.

Main Methods:

• Recording 13C-NMR spectra of high-spin met-aquo, spin-equilibrium met-azido, low-spin met-cyano, deoxy, and carbonmonoxy myoglobin.
• Utilizing 1H decoupling techniques to resolve and assign 13C signals.
• Enriching hemin with 13C at vinyl alpha or beta positions for enhanced signal detection.
• Analyzing hyperfine shifts and comparing them with model complexes.

Main Results:

• Resolved 13C-NMR spectra were obtained within approximately 15 minutes for enriched myoglobin samples.
• Specific assignments of vinyl 13C alpha signals were achieved for paramagnetic derivatives, and 13C beta signals for met-cyano myoglobin.
• Hyperfine shift patterns indicate dominant pi contact shifts in ferric complexes, with greater in-plane asymmetry in myoglobin compared to model complexes.
• Deoxy myoglobin data suggest limited pi bonding involving vinyl groups.

Conclusions:

• 13C-NMR spectroscopy is effective for characterizing vinyl groups in myoglobin derivatives.
• The electronic structure of myoglobin's heme vinyl groups exhibits distinct features related to its protein environment.
• The findings contribute to a deeper understanding of heme protein electronic properties and structure-function relationships.