NDLI: Role of globin moiety in the autoxidation reaction of oxymyoglobin: effect of 8 M urea.

Content Provider	PubMed Central
Author	Sugawara, Y. Matsuoka, A. Kaino, A. Shikama, K.
Abstract	It is in the ferrous form that myoglobin or hemoglobin can bind molecular oxygen reversibly and carry out its function. To understand the possible role of the globin moiety in stabilizing the FeO2 bond in these proteins, we examined the autoxidation rate of bovine heart oxymyoglobin (MbO2) to its ferric met-form (metMb) in the presence of 8 M urea at 25 degrees C and found that the rate was markedly enhanced above the normal autoxidation in buffer alone over the whole range of pH 5-13. Taking into account the concomitant process of unfolding of the protein in 8 M urea, we then formulated a kinetic procedure to estimate the autoxidation rate of the unfolded form of MbO2 that might appear transiently in the possible pathway of denaturation. As a result, the fully denatured MbO2 was disclosed to be extremely susceptible to autoxidation with an almost constant rate over a wide range of pH 5-11. At pH 8.5, for instance, its rate was nearly 1000 times higher than the corresponding value of native MbO2. These findings lead us to conclude that the unfolding of the globin moiety allows much easier attack of the solvent water molecule or hydroxyl ion on the FeO2 center and causes a very rapid formation of the ferric met-species by the nucleophilic displacement mechanism. In the molecular evolution from simple ferrous complexes to myoglobin and hemoglobin molecules, therefore, the protein matrix can be depicted as a breakwater of the FeO2 bonding against protic, aqueous solvents.
Related Links	http://dx.doi.org/10.1016/s0006-3495(95)79932-5
Ending Page	592
Page Count	10
Starting Page	583
File Format	PDF
ISSN	00063495
e-ISSN	15420086
Journal	Biophysical Journal
Issue Number	2
Volume Number	69
Language	English
Publisher Date	1995-08-01
Access Restriction	Open
Subject Keyword	Biophysics Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Biophysics

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