How are our enzymes able to perform quantum tunnelling?

The probability of quantum-mechanical tunneling through a barrier depends on the energy involved in the barrier. For two protons to fuse requires overcoming an energy barrier of many millions of electron-volts. By contrast, energy barriers to configuration changes in atoms and molecules are typically a few electron-volts or even a fraction of an electron-volt.

Quantum-mechanical tunneling can occur in enzymes at room temperature because the energy barriers are comparable to thermal energies at room temperature, a few milli-electron-volts.