Hydrogen ion equilibria in fish haemoglobins

Area of Science:

• Comparative biochemistry
• Physiological chemistry

Background:

• Hemoglobin (Hb) is crucial for oxygen transport in vertebrates.
• Understanding Hb-H+ (hydrogen ion) equilibria provides insights into respiratory physiology.
• Species-specific differences in Hb structure and function are key to adaptation.

Purpose of the Study:

• To investigate and compare H+ titration and buffer values of oxygenated and deoxygenated hemoglobins across different vertebrate species.
• To correlate Hb buffer values with histidine content and structural features.
• To analyze the relationship between buffer values and the fixed-acid Haldane effect.

Main Methods:

• Performed H+ titration studies on hemoglobins from carp, rainbow trout, spiny dogfish, and pig.
• Compared experimental data with existing Hb-H+ equilibria and amino acid sequence information.
• Analyzed buffer values in relation to histidine residue and alpha-amino group content.

Main Results:

• Teleost hemoglobins (carp, trout) exhibit significantly lower buffer values than elasmobranch (dogfish) and mammalian (pig) hemoglobins.
• Lower buffer values in teleosts correlate with reduced histidine and alpha-amino group content.
• An inverse relationship exists between buffer values and the fixed-acid Haldane effect, with carp and trout showing the largest effect and dogfish the smallest.

Conclusions:

• Species-specific histidine content is a primary determinant of hemoglobin buffer values.
• Teleost hemoglobins possess unique H+ binding characteristics influencing their respiratory function.
• Pig hemoglobin displays intermediate H+ equilibria, bridging teleost and elasmobranch types.