Dissociation and auto-oxidation of hemerythrin induced by SH-modification: a kinetic study.
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-1.s-1. The dissociation and auto-oxidation followed first-order kinetics with rate constants of 4 X 10(-3) s-1 and 5 X 10(-4) s-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.
Fuseya
M
M
Department of Chemistry, Faculty of Science, Science University of Tokyo.
Ichimura
K
K
Yamamura
T
T
Tachi'iri
Y
Y
Satake
K
K
Amemiya
Y
Y
Kihara
H
H
D000818:Animals; D002942:Circular Dichroism; D003063:Cnidaria; D006422:Hemerythrin / Q000302:isolation & purification* / Q000378:metabolism; D007700:Kinetics; D008667:Metalloproteins / Q000302:isolation & purification*; D010084:Oxidation-Reduction; D011487:Protein Conformation; D012542:Scattering, Radiation; D013056:Spectrophotometry, Ultraviolet; D013438:Sulfhydryl Compounds / Q000378:metabolism; D013997:Time Factors; D014965:X-Rays
D006422:Hemerythrin; D008667:Metalloproteins; D013438:Sulfhydryl Compounds