A protonophore, also known as a proton translocator, is an ionophore

Ionophore

An ionophore is a lipid-soluble molecule usually synthesized by microorganisms to transport ions across the lipid bilayer of the cell membrane...

 that allows proton

Proton

The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

s to cross lipid bilayer

Lipid bilayer

The lipid bilayer is a thin membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around cells. The cell membrane of almost all living organisms and many viruses are made of a lipid bilayer, as are the membranes surrounding the cell nucleus...

s. This would otherwise not occur as protons have positive charge and hydrophilic properties, making them unable to cross without a channel

Ion channel

Ion channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of cells by allowing the flow of ions down their electrochemical gradient. They are present in the membranes that surround all biological cells...

 or transporter. Protonophores are generally aromatic compounds that are both hydrophobic and capable of distributing the negative charge over a number of atoms by π-orbital

Atomic orbital

An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus...

s which delocalize a proton's charge in the molecule. Both the neutral and the charged species can diffuse across the lipid bilayer by passive diffusion and simultaneously facilitating proton transport.

Representative protonophores include:

• 2,4-dinitrophenol
  2,4-Dinitrophenol
  2,4-Dinitrophenol , C6H4N2O5, is a cellular metabolic poison. It uncouples oxidative phosphorylation by carrying protons across the mitochondrial membrane, leading to a rapid consumption of energy without generation of ATP....
  
  
• Carbonyl cyanide-p-trifluoromethoxyphenylhydrazone
  Carbonyl cyanide-p-trifluoromethoxyphenylhydrazone
  Carbonyl cyanide-p-trifluoromethoxyphenylhydrazone is an ionophore that is a mobile ion carrier. It referred to as an uncoupling agent because it disrupts ATP synthesis by transporting hydrogen ions through a cell membrane before they can be used to provide the energy for oxidative...
  
   (FCCP)
• Carbonyl cyanide m-chlorophenyl hydrazone
  Carbonyl cyanide m-chlorophenyl hydrazone
  Carbonyl cyanide m-chlorophenyl hydrazone , is a chemical inhibitor of oxidative phosphorylation. It is a nitrile, hydrazone and ionophore. In general, CCCP causes the gradual destruction of living cells and death of the organism. The CCCP affects the protein synthesis reactions in seedling...
  
  (CCCP)

Mechanism of action

The facilitated transport of protons across the biological membrane by protonophore is achieved as follows.

1. The anionic form of the protonophore (P^-) is absorbed onto one side (Positive) of the biological membrane.
2. Protons (H⁺) from the aqueous solution combine with the anion (P^-) to produce the neutral from (PH)
3. PH diffuses across the biological membrane and dissociates into H⁺ and P^- on the other side.
4. This H⁺ is released from the biological membrane into the other aqueous solution
5. P^- returns to the first side of the biological membrane by electrophoresis (its electrostatic attraction to the positive side of the membrane).