Carp hemoglobin. II. The alkaline Bohr effect

Area of Science:

• Biochemistry
• Physiological Chemistry
• Protein Chemistry

Background:

• The Bohr effect describes the influence of pH on hemoglobin's oxygen affinity.
• Carp hemoglobin's Bohr effect is critical for efficient oxygen transport and carbon dioxide buffering in fish.
• Understanding these effects is key to comprehending hemoglobin's physiological role.

Purpose of the Study:

• To quantitatively determine the Bohr effect of carp hemoglobin across a wide pH range.
• To investigate the influence of various buffers (bis-Tris, phosphate) and ions (inositol, NaCl) on the Bohr effect.
• To elucidate the relationship between cooperativity, pH, and proton release in carp hemoglobin.

Main Methods:

• Differential titration
• Direct acid-base titration
• Oxygen equilibrium analysis
• Precise pH variation studies

Main Results:

• Carp hemoglobin releases 3.7 protons at pH 6.9 in the absence of ions.
• Phosphate buffer (0.1 M) increases proton release to 6.1 at pH 7.25.
• Inositol addition lowers the Bohr effect magnitude and shifts its optimum pH higher.
• High salt concentrations (2.5 M NaCl) increase the number of oxygen-linked groups.
• Proton release is linear with ligand saturation at high cooperativity (phosphate buffer).

Conclusions:

• Carp hemoglobin exhibits a versatile Bohr effect modulated by pH and ionic environment.
• The protein's functional versatility suggests mechanisms for regulating CO2 transport via allosteric interactions.
• Buffer type and ionic strength significantly impact the magnitude and pH optimum of the Bohr effect in carp hemoglobin.