Nitrogen-fixing bacteria use an enzyme called nitrogenase to split molecules of nitrogen gas (N₂) and combine the atoms with hydrogen (H₂).

Here's a breakdown:

* Nitrogenase is a complex enzyme with multiple components. The key component is a molybdenum-iron protein (MoFe protein) that contains a special active site.

* The active site of nitrogenase contains a cluster of atoms, including molybdenum, iron, and sulfur, which are crucial for breaking the strong triple bond in the nitrogen molecule.

* The process involves several steps, but essentially, the nitrogenase enzyme binds to a nitrogen molecule and uses electrons and protons (from hydrogen) to break the bond and form ammonia (NH₃). This process requires a significant amount of energy, which is supplied by the bacteria through metabolic pathways.

Here's a simple equation for the reaction:

N₂ + 8H⁺ + 8e^- → 2NH₃ + H₂

This reaction is fundamental for life on Earth, as it provides the nitrogen necessary for building proteins and nucleic acids.