Dissociation and Auto-Oxidation of Hemerythrin Induced by SH-Modification: A Kinetic Study

• Published in: Journal of biochemistry (Tokyo) 1989-02, Vol.105 (2), p.293-298
• Main Authors: Fuseya, Moriyasu, Ichimura, Kaoru, Yamamura, Takaki, Tachi, Yoshiaki, Satake, Kazuo, Amemiya, Yoshiyuki, Kihara, Hiroshi
• Format: Article
• Language: English
• Subjects: Analytical, structural and metabolic biochemistry; Animals; Biological and medical sciences; Circular Dichroism; Cnidaria; Fundamental and applied biological sciences. Psychology; Hemerythrin - isolation & purification; Hemerythrin - metabolism; Kinetics; Metalloproteins; Metalloproteins - isolation & purification; Other metalloproteins; Oxidation-Reduction; Protein Conformation; Proteins; Scattering, Radiation; Siphonosoma cumanense; Spectrophotometry, Ultraviolet; Sulfhydryl Compounds - metabolism; Time Factors; X-ray scattering; X-Rays
• ISSN: 0021-924X; 1756-2651
• DOI: 10.1093/oxfordjournals.jbchem.a122656

Hemerythrin from Siphonosoma cumanense has a trimeric structure consisting of identical subunits, which have no cooperativity nor Bohr effect on oxygen-binding. The trimer was dissociated into its monomers by the modification of the SH group of its cysteines with p-chloromercuriphenylsulfonic acid (PCMPS), which was monitored by stopped-flow of both spectrophotomeric and small angle X-ray scattering methods. The results showed that the process involved sequential modification of the SH groups, dissociation into monomers, and auto-oxidation of ferrous iron in the active center. The modification of the SH groups with PCMPS followed second-order kinetics with a rate constant of 1.8 M−18−1. The dissociation and auto-oxidation followed first-order kinetics with rate constants of 4 × 10−3 8−1and 5 × 10−4 8−1 respectively. The obtained rate of auto-oxidation was much faster than that in the native state. These findings lead to the conclusion that the trimeric state of S. cumanense hemerythrin is necessary to prevent auto-oxidation.