Nitrogenase - Similarity To Other Proteins

Similarity To Other Proteins

The three subunits of nitrogenase exhibit significant sequence similarity to three subunits of the light-independent version of protochlorophyllide reductase that performs the conversion of protochlorophyllide to chlorophyll. This protein is present in gymnosperms, algae, and photosynthetic bacteria but has been lost by angiosperms during evolution.

Separately, two of the nitrogenase subunits (NifD and NifD) have homologues in methanogens that do not to fix nitrogen e.g. Methanocaldococcus jannaschii. Little is understood about the function of these "class IV" nif genes, though they occur in many methanogens. In M. jannaschii they are known to interact with each other and are constitutively expressed.