The fixABCX operon in E. coli contains four genes which encode for proteins that are potentially used in the anaerobic metabolism of carnitine, similar to those in the caiTABCDE operon. This operon can be activated by the cAMP-activated global transcriptional regulator CRP. Both the fix and cai operons are expressed in anaerobic conditions to metabolize carnitine, and they are found very close to one another in the genome, in opposite directions. The first gene, fixA, encodes for a protein which, with the protein produced by fixB, form a heterodimer protein. This protein may work as an electron transfer proteins, due to their similarity to electron transport flavoproteins in mammals. The third gene, fixC, encodes a protein that may be part of an electron transfer system in the anaerobic metabolism of carnitine. The final gene, fixX, encodes a ferredoxin-like protein involved in carnitine reduction.

Operon: Redox Process References