text: Before a 2007 report by Alber and coworkers, crotonyl-coA carboxylases and reductases (CCRs) 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 (2S)-ethyl malonyl-coA which was a favorable reaction. The specific CCR homolog came from the bacterium Rhodobacter sphaeroides.