Homology of the NifS family of proteins to a new class of pyridoxal phosphate‐dependent enzymes

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Abstract
Iterative profile sequence analysis reveals a remote homology of peroxisomal serine‐pyruvate aminotransferases from mammals to the small subunit of soluble hydrogenases from cyanobacteria, an isopenicillin N epimerase, the NifS gene products from bacteria and yeast, and the phosphoserine aminotransferase family. All members of this new class whose function is known are pyridoxal phosphate‐dependent enzymes, yet they have distinct catalytic activities. Upon alignment, a lysine around position 200 remains invariant and is predicted to be the pyridoxal phosphate‐binding residue. Based on the detected homology, it is predicted that NifS has also a pyridoxal phosphate‐dependent serine (or related) aminotransferase function associated with nitrogen economy and/or protection during nitrogen fixation.