Before a 2007report 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 specific CCR homolog was able to reduce crotonyl-CoA to -ethyl malonyl-CoA which was a favorable reaction. The specific CCR homolog came from the bacterium Rhodobacter sphaeroides.