The reversible binding of oxygen to sulfhemoglobin

Area of Science:

• Biochemistry
• Physiology
• Hematology

Background:

• Sulfhemoglobin is a hemoglobin variant with altered oxygen-binding properties.
• Understanding sulfhemoglobin's O2 affinity and Bohr effect is crucial for diagnosing and managing related conditions.

Purpose of the Study:

• To investigate the oxygen (O2) binding characteristics of sulfhemoglobin.
• To compare sulfhemoglobin's O2 affinity, Bohr effect, and cooperativity with hemoglobin A.

Main Methods:

• Measurement of oxygen tension for half-saturation (P50) of sulfhemoglobin.
• Analysis of the Bohr effect and Hill number for sulfhemoglobin.
• Preparation and O2 binding studies of sulfhemoglobin from carboxypeptidase A-treated hemoglobin.

Main Results:

• Sulfhemoglobin requires >100-fold higher oxygen tension for half-saturation compared to hemoglobin A.
• Sulfhemoglobin exhibits an alkaline Bohr effect larger than hemoglobin, with a Hill number of 1.
• 0.68 protons are released per O2 bound at 0°C, and cooperativity is absent, similar to its precursor.

Conclusions:

• Sulfhemoglobin demonstrates pH-dependent oxygen affinity, behaving as a high-affinity form at alkaline pH and low-affinity at acidic pH.
• The Hill number is not a definitive indicator of oxygen binding interactions in hemoglobin variants.
• These findings provide insights into the functional consequences of sulfhemoglobin formation.