The purpose of electron transport systems is to conduct a stepwise release of energy from redox reactions that can be coupled to work (e. g., extrusion of protons). During electron transfer, a series of non-protein cofactors undergoes reversible reduction and oxidation with small transition states to avoid loss of energy as heat. Which of the molecular features listed below facilitate the low energy transitions mediated by the redox centers? Choose one or more:

A. coenzyme A (e. g., in Acetyl-CoA)

B. phosphoryl groups with high energy of hydrolysis (e. g., ATP)

C. conjugated double-bond and heteroaromatic rings (e. g., in FMN and NAD+)

D. metal ions (e. g., Fe-S clusters) E. heme groups