302 disulfide cross-links Chen , 2008 - pKa 7 - H2S HS- McCartney Oleszkiewicz, 1991 - 7 8 50 90 IC50 30-250 Lens , 1998 Omil , 1996 Parkin 1990 100-800 O'Flaherty , 1998) - Fe2+ Fe3+ FeCl3 FeSO42 6.4 6.5 Ryckebosch , 2011