Disclosed are trans-enoyl CoA reductase (TER) enzymes and nucleic acids encoding them. In some cases, the TER enzymes are non-natural, engineered trans-enoyl CoA reductase. TER enzymes were shown to catalyse the conversion of 5-carboxy-2-pentenoyl-CoA into adipyl-CoA for improved adipate production and the conversion of crotonyl-CoA into 6-aminocaproate. The enzymes can be used in biosynthetic methods and engineered microorganisms that enhance or improve the biosynthesis of 6-aminocaproate, hexamethylenediamine, caproic acid, caprolactone, or caprolactam. The engineered microorganisms include exogenous TER and in some cases engineered TER.