Before a 2007 report by Alber and coworkers, crotonyl-CoA carboxylases and reductases were known for reducing crotonyl-CoA to butyryl-CoA. A report by Alber and coworkers concluded that a specificCCRhomolog was able to reduce crotonyl-CoA to -ethyl malonyl-CoA which was a favorablereaction. The specific CCR homolog came from the bacterium Rhodobacter sphaeroides.