PROS1 and hydrops fetalis: Furthermore, hepcidin and the iron regulatory proteins 1 and 2 (IRP1 and IRP2) as well as aconitase activity (that reflects amount of IRP1 protein containing 4S-4Fe cluster and thus deprived of IRE binding capacity), jointly responsible for the regulation of expression of iron handling proteins, were unchanged in HF rats (Fig. 4E–H).