<Tr> <Th> NCBI </Th> <Td> proteins </Td> </Tr> <P> Nitrogenases are enzymes (EC 1.18. 6.1 EC 1.19. 6.1) that are produced by certain bacteria, such as cyanobacteria (blue - green algae). These enzymes are responsible for the reduction of nitrogen (N) to ammonia (NH). Nitrogenases are the only family of enzymes known to catalyze this reaction, which is a key step in the process of nitrogen fixation . Nitrogen fixation is required for all forms of life, with nitrogen being essential for the biosynthesis of molecules (nucleotides, amino acids) that create plants, animals and other organisms . </P> <P> The equilibrium formation of ammonia from molecular hydrogen and nitrogen has an overall negative enthalpy of reaction (Δ H 0 = − 45.2 k J m o l − 1 N H 3 (\ displaystyle \ Delta H ^ (0) = - 45.2 \ \ mathrm (kJ) \, \ mathrm (mol ^ (- 1)) \; \ mathrm (NH_ (3)))), the activation energy is very high (E A = 230 − 420 k J m o l − 1 (\ displaystyle E_ (A) = 230 - 420 \ \ mathrm (kJ) \, \ mathrm (mol ^ (- 1)))). Nitrogenase acts as a catalyst, reducing this energy barrier such that the reaction can take place at ambient temperatures . </P> <P> The nitrogenase complex consists of two proteins: </P>

A metal ion necessary for the functioning of an enzyme is known as a