The siderophore coprogen is tansported in N. crassa as an entity. Neither ligand exchange nor reduction is a rate limiting step for intracellular accumulation. Metabolized iron was found predominantly to exist as fast relaxing Fe(II) high-spin (σ=1.32 mm/s, ΔEQ=2.95 mm/s) and Fe(III) high-spin species (δ=0.35-0.42 mm/s ΔEQ=0.5-0.58 mm/s). Within 27 hours, no measurable amounts of iron are transferred to ferritin like storage forms. Rather, coprogen itself serves as an intermediate iron storage compound.