It is also possible that this initial proton transfer will prompt the transfer of a second proton belonging to the other base, with the final product being two neutrally charged bases, each with misplaced hydrogen atoms (see Figure ). This double proton transfer is known as tautomerisation, and each tautomeric base is known as a tautomer. The overall tautomerisation mechanism can be written: A-T ↔ A*-T*, G-C ↔ G*-C* (where '*' denotes a tautomer).