Superoxide-Dependent Nitrogenase

Abstract

Nitrogen is one of the essential elements of all forms of life. The Earth’s atmosphere contains nearly 79% dinitrogen (N2), however, this inert gaseous compound cannot be directly utilized by most living organisms, such as plants, animals, and human beings. Very few prokaryotes (members of the bacteria and the archaea) of diverse phylogenic origin and physiological groups possess the ability to “fix” gaseous dinitrogen (N2) and convert it into compounds, which when combined with oxygen or hydrogen can be utilized by the remaining organisms living on the Earth. This reaction, performed exclusively by prokaryotes, is termed “nitrogen fixation” and the enzyme complex essential for this reaction is called “nitrogenase”. This enzyme consists of two proteins, an iron protein and a molybdenum-iron protein. Both proteins from “conventional” nitrogenase complexes are highly sensitive to O2. Streptomyces thermoautotrophicus is also able to fix dinitrogen, but it harbors a very unusual N2-fixing system, which differs in many respects from the “conventional“ nitrogenases.