Complex sentence: Free cyano and carbonyl ligands are toxic to many biological systems so their inclusion in this system suggests they play pivotal role, perhaps insuring the irons at the active site remain in a low spin state throughout the catalytic cycle.
Split into simpler sentences: Free cyano and carbonyl ligands are toxic to many biological systems so their inclusion in this system suggests they play pivotal role. This high field ligands may insure the iron centers at the active site remain in a low spin state throughout the catalytic cycle.