Electric Potentials Due to CO₂ Diffusion in Myoglobin Solutions

Summary

The passage of CO₂ through water layers is attended by concurrent transport of (bi)carbonate. Since both bicarbonate and carbonate are charged molecules, their diffusion may evoke electric potentials and thus there will be interaction with all other ions present in the solution. Such effects have been described in the literature for weak acids and protein solutions of hemoglobin and albumin (Stroeve et al., 1985). Here, we present measurements of electric potential difference across layers containing 1.5 mmol/1 myoglobin at 25° C and various amounts of Na⁺ ions, where chemical equilibrium for the hydration reaction of CO₂ was achieved by adding carbonic anhydrase. Voltages measured ranged from up to 5 mV at zero cation concentration to 0.7 mV around 100–150 mmol/1 [Na⁺]. Contrary to hemoglobin and albumin, these voltages are lower, and even much lower, than theoretical predictions.