Complex sentence: Sulfite is with high affinity reduced by sulfite reductase with ferredoxin as a reductant and the formed sulfide is incorporated into cysteine, catalyzed by O-acetylserine (thiol) lyase, with O-acetylserine as substrate.
Split into simpler sentences: Sulfite is with high affinity reduced by sulfite reductase to sulfide with ferredoxin as a reductant. Sulfide is incorporated into cysteine, catalyzed by O-acetylserine (thiol) lyase, with O-acetylserine as substrate.