What is Nitrogenase?

As an enzyme that is employed by some organisms to fix the presence of nitrogen in the atmosphere, nitrogenase helps to maintain the balance of compounds within the air that we breathe, preventing an overabundance of nitrogen (N2) and making the planet uninhabitable for human beings. Here is some background on how nitrogenase works, and what can happen when the process is employed.

Nitrogenase is essential in the process of breaking down what is known as the triple bond that occurs with nitrogen atoms. Essentially, each atom of nitrogen contains a series of three orbitals that are part of the atom shell. As two atoms of nitrogen bond with one another, the orbitals also bond. Thus, splitting the two bonded nitrogen atoms also means separating the orbitals. Nitrogenase accomplishes this by obtaining donors of electrons from each of the three orbitals. While each orbital is broken down individually, the process is not complete until all three have been separated. While the complete process of accomplishing this separation is not understood, it is known that nitrogenase utilizes both MoFe protein and ATP in order to generate the energy to effect the separation.

As the atoms are broken down, nitrogenase acts as the catalyst to cause each atom to bond with three atoms of hydrogen, forming ammonia. The ammonia in turn is bonded with glutamate to form glutamine. Generally, it is assumed that three cycles are required to result in the formation of atmospheric nitrogen gas, although some experts differ on the exact number of cycles required.

The study of how nitrogenase functions is an ongoing process, owing to the difficulty in obtaining crystals of nitrogen that are bound to nitrogenase. It is known that nitrogenase has the ability to bond acetylene and carbon monoxide, and that dinitrogen is an example of a substrate that is competitive for the binding of acetylene. Dinitrogen, commonly referred to as laughing gas or nitrous oxide, inhibits the binding of acetylene to nitrogen atoms and thus prevents the interference of the bonding between nitrogen atoms and hydrogen.

Most forms of nitrogenase are inhibited by the presence of dioxygen, although there are always new discoveries that challenge this. At least one form of nitrogenase, referred to as streptomyces thermautotrophicus, is not subject to the effects of any type of oxygen. While there is still a great deal to discover about how nitrogenase works to create the atmosphere that much of life relies upon, there can be no doubt that without the presence of enzymes like nitrogenase in our atmosphere, life as we know it would cease to exist.