In plant photosynthesis, water molecules are photo-oxidized to release oxygen and protons.

Potassium hydrogen phosphate releases protons in aqueous solution, resulting in a pH of about 4, making the silk acidic and thus protecting it from fungi and bacteria that would otherwise digest the protein.

Thus, this bicyclic structure can serve as an electron buffer pool to release or absorb protons to maintain the pH near the membranes.

Conversely, in the lungs, where oxygen concentration is high, binding of oxygen causes hemoglobin to release protons, which combine with bicarbonate to drive off carbon dioxide in exhalation.

It can also be a compound such as aluminium sulfate, which reacts in the soil to release protons.

It uncouples oxidative phosphorylation in cartilaginous (and hepatic) mitochondria, by diffusing from the inner membrane space as a proton carrier back into the mitochondrial matrix, where it ionizes once again to release protons.

Instead, it reacts with water molecules acting as a Lewis acid, releasing protons.