Oxygen fluorescence quenching studies with single tryptophan-containing proteins

Area of Science:

• Biochemistry
• Biophysics
• Protein Science

Background:

• Molecular oxygen is a known quencher of tryptophan fluorescence in proteins, as established by Lakowicz and Weber.
• Tryptophan fluorescence is a crucial tool for studying protein structure and dynamics.

Purpose of the Study:

• To investigate the oxygen quenching of tryptophan fluorescence in proteins with single, internal tryptophan residues.
• To quantify the dynamic quenching rate constants (kq) and assess the degree of static quenching in these proteins.

Main Methods:

• Fluorescence intensity and phase lifetime measurements were used to study oxygen quenching.
• The study examined apoazurin (Pseudomonas aeruginosa), asparaginase (Escherichia coli), ribonuclease T1 (Aspergillus oryzae), and cod parvalbumin.

Main Results:

• A significant degree of apparent static quenching was observed in the studied proteins.
• The dynamic quenching rate constants (kq) were found to be lower than those reported for other proteins.
• The apparent kq for apoazurin was determined to be 0.59×10(9) M(-1)s(-1) at 25°C, the lowest reported value.

Conclusions:

• The internal environment of tryptophan residues in these proteins influences oxygen quenching dynamics.
• The low kq values suggest restricted accessibility of the tryptophan residue to molecular oxygen.
• These findings provide insights into the structural and dynamic properties of proteins affecting fluorescence quenching.