I. Proton transfer to terminal and bridging oxo ligands. II. Iron binding to the apoprotein of horse spleen ferritin

Part I: Proton transfers to terminal and bridging oxo ligands . Protonation of terminal and bridging oxo ligands is proposed in the mechanistic cycles of several metalloenzymes. A knowledge of the rate constants of proton transfer to and from these ligands, as well as of the pKa of the protonated ligands, is useful when predicting mechanistic details of enzyme action. For this purpose, the proton transfer reactions of an oxo-bridged complex [Fe(OEP)]2O (OEP is octaethylporphyrin) and a terminal hydroxo manganese complex K[MnIII (H3L)(OH)] (L is tris[N'-tert-butylureaylato)- N-ethyl]amine) were examined. The rate constant for deprotonation of K[MnIII(H3L)(OH)] by KOtBu in DMSO was determined as 2.2(2)x104 M-1s -1 at 25 °C. The mechanistic details of the deprotonation were also considered.; Part II: Iron binding to the apoprotein of horse spleen ferritin . Ferritin is a ubiquitous iron mineralization protein which plays an important role in iron storage and detoxification. There are numerous reports on the rate at which different types of ferritins oxidize Fe(II); however, the thermodynamics of iron binding to the protein prior to oxidation have been little investigated. The equilibrium constant for Fe(H) binding by apo horse spleen ferritin has been estimated as 3.0(5)x10 5 M-1 at 25 °C. The possible binding sites and the number of iron atoms bound per H chain have also been analyzed.