Complex sentence: The APS-sulfite redox couple has a "E" 0' of -60 mV that allows APS to be reduced by either NADH or reduced ferrodoxin using the enzyme adenylyl-sulfate reductase (Apr), which requires the input of 2 electrons.
Split into simpler sentences: The APS-sulfite redox couple has a "E" 0' of -60 mV that allows APS to be reduced by either NADH or reduced ferrodoxin. APS is reduced to sulfite by the enzyme adenylyl-sulfate reductase (Apr) that requires the input of 2 electrons.