Nitrogenases
Definition and meaning of Nitrogenases in chemistry.
Nitrogenases are complex enzymes produced by certain bacteria to break down nitrogen gas in the air. They turn this stubborn N2 gas into ammonia so that plants and animals can actually use it. They are the only enzymes on Earth capable of performing this vital chemical transformation.
In more detail
Nitrogen gas (N2) makes up about seventy-eight percent of the air we breathe daily. However, plants and animals cannot use this raw N2 directly for their biological growth. The two nitrogen atoms are locked together by an incredibly strong chemical triple bond.
Nitrogenases are the specialized biological machines that crack this tough triple bond apart. They use a unique protein containing iron (Fe) and molybdenum (Mo) metals to do the heavy lifting. Breaking the bond requires a massive amount of cellular energy in the form of ATP.
The enzyme also needs extra electrons to safely attach hydrogen atoms to the nitrogen atoms. This specific process creates ammonia (NH3), which acts as a vital natural fertilizer for the soil. A major problem is that normal oxygen gas (O2) easily destroys all nitrogenase enzymes.
The O2 quickly reacts with the metals inside and permanently breaks the delicate enzyme structure. To fix this issue, bacteria have developed clever ways to hide the enzyme from oxygen. Some bacteria live inside thick plant root nodules that physically block out the surrounding air.
Other bacteria create thick slime layers or use special proteins to sponge up nearby O2. Without these careful biological protections, the global nitrogen cycle would completely grind to a halt. Virtually all life on Earth depends heavily on this hidden and highly sensitive bacterial chemistry.
Key facts
| Field | Biochemistry |
|---|---|
| Substrate | N2 |
| Product | NH3 |
| Cofactor | FeMoco |
| Energy source | Requires 16 molecules of ATP per reaction |
| Greatest weakness | Highly sensitive to oxygen gas (O2) |
The bacteria Rhizobium leguminosarum live inside the roots of bean and pea plants. They use their nitrogenase enzymes to pull N2 gas directly from the soil air. The bacteria feed the resulting NH3 to the plant to help it grow big and strong.
Frequently asked questions
Why do plants need bacteria to get nitrogen?
Plants simply do not have the right enzymes to break the strong triple bond in N2. Only specific bacteria possess the nitrogenase enzymes required to successfully perform this very difficult task.
What happens if oxygen touches the nitrogenase enzyme?
The O2 gas quickly reacts with the exposed iron and molybdenum metal clusters inside the enzyme. This unwanted oxidation reaction permanently destroys the enzyme and completely stops all nitrogen fixing.
What is the overall biological chemical reaction?
The reaction is N2 + 8H+ + 8e- + 16ATP yields 2NH3 + H2 + 16ADP + 16Pi. This means it takes immense energy and eight electrons to split just one nitrogen molecule.