One electron reduction of metmyoglobin and methemoglobin and the reaction of the reduced molecule with oxygen

Y. A. Ilan*, J. Rabani, G. Czapski

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Scopus citations

Abstract

We have used the pulse radiolysis technique to reduce with solvated electrons (eaq-) a single Fe(III) site in methemoglobin and metmyoglobin. The reduction process was followed spectrophotometrically and the reactions rate constants were measured: keaq- + methemoglobin 6.5 ± 1 · 1010M-1·s-1·kea q- + metmyoglobin 2.5 ± 0.3·1010M-1·s-1. Approx. 60% of the eaq have reacted with the hemin group, and the rest of the eaq- have probably reacted with the globin moiety. We followed the reaction of the reduced proteins to yield the oxyderivatives and measured the rate constants of the oxygenation processes kreduced methemoglobin + O2 2.6 ± 0.6·107 M-1·s-1 and kmyoglobin + O2 1.8 ± 0.2·107 M-1 ·s-1, All the rate constants were measured at pH 6.8, I 0.004, T 22 ± 2 °C. The high rate constant for reduced methemoglobin indicates that one-site-reduced methemoglobin is probably in the R state, as predicted for methemoglobin from X-ray analysis. The spectra of the reduced and oxygenated species were measured under similar conditions at λ 450-650 nm. We were able to follow slight changes in the micro-second time scale, these changes were attributed to conformational changes. We were not able to detect any reaction between the radical O2- and the hemin group (which would result in a complex such as heme -O2). This may be due to kinetic reasons.

Original languageEnglish
Pages (from-to)277-286
Number of pages10
JournalBBA - Protein Structure
Volume446
Issue number1
DOIs
StatePublished - 28 Sep 1976

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