Kinetics and mechanisms of the oxidation of myoglobin by Fe(III) and Cu(II) complexes

• Published in: Biochimica et biophysica acta Vol. 912; no. 3; pp. 384 - 397
• Main Authors: Hegetschweiler, Kaspar, Saltman, Paul, Dalvit, Claudio, Wright, Peter E.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 30.04.1987; Elsevier; North-Holland
• Subjects: Binding Sites; Biological and medical sciences; Copper - metabolism; Copper(II) reduction; Electrochemistry; Electron Transport; Ferric Compounds - metabolism; Fundamental and applied biological sciences. Psychology; Hydrogen-Ion Concentration; Iron(III) reduction; Kinetics; Magnetic Resonance Spectroscopy; Molecular biophysics; Myoglobin - metabolism; Myoglobin oxidation kinetics; Nickel - metabolism; Nitrilotriacetic Acid; Osmolar Concentration; Oxidation-Reduction; Physical chemistry in biology; Zinc - metabolism; Copper(II) reduction; HbO 2; MbCO; Hepes; Bistris; Myoglobin oxidation kinetics; CDTA; deoxyHb; Mb; Iron(III) reduction; Hb; NTA; Electron transport; MetMb; Iron «III» Complexes; Myoglobin; Sperm whale; Vertebrata; Hemoprotein; Mammalia; Copper II Complexes; Electron transfer; Oxidation; Cetacea; Kinetics
• ISSN: 0167-4838; 0006-3002; 1879-2588; 1878-2434
• DOI: 10.1016/0167-4838(87)90043-4

Two distinct mechanisms by which sperm whale myoglobin reduces, respectively, complexes of Fe(III) and Cu(II) and, in turn, is oxidized to metmyoglobin have been characterized. For both mechanisms, deoxymyoglobin is the active reductant. An outer sphere electron transfer, probably at the edge of the heme, is involved for Fe(III)NTA (NTA is nitrilotriacetic acid. This pathway does not involve ionic binding of the Fe(III) complex to the protein. The most reactive species of Fe(III)NTA is uncharged. No inhibition is observed with Ni(II) or Zn(II). An outer sphere site specific electron transfer is operative for reduction of Cu(II) complexes. The site has been characterized using NMR spectroscopy and involves one or more histidines. There is an initial binding of the Cu(II) chelate. The ternary complex of chelator-Cu(II)-deoxymyoglobin is a mandatory intermediate. Ni(II) and Zn(II) compete with Cu(II) for the binding site. A scheme for the participation of either or both of these mechanisms in reduction reactions of heme proteins is proposed. Both the overall redox potential, ΔE 0, and the stability constant for the ternary complex, K, govern the pathway and the reaction rate.