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Water Relaxation Measurements on Semiquinones of Various Flavoproteins

✍ Scribed by Antonie J. W. G. Visser; Jan L. De Wit; Franz Müller; Herman J. C. Berendsen

Publisher
John Wiley and Sons
Year
1982
Tongue
German
Weight
516 KB
Volume
65
Category
Article
ISSN
0018-019X

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✦ Synopsis

Abstract

The water relaxation rates of several flavoproteins in the semiquinone state have been investigated by the spin echo technique. The results indicate a rather unspecific interaction between water and the protein‐bound flavosemiquinones. An average interaction distance of 0.3‐0.5 nm has been estimated. From the temperature dependence of the rate constants the free energy of activation for proton exchange is calculated to be about 17 kJ/mol. The rate of proton exchange is around 10^11^ s−^1^ for the flavosemiquinones investigated are accessible to water regardless of their ionic state.

The large difference in relaxation rates of water protons between D‐ and L‐ amino‐acid oxidases is noticeable. Oxynitrilase exhibits the highest whereas Azotobacter vinelandii flavodoxin shows the lowest water relaxation rate of the flavoproteins studied. The results are discussed in relation to the visible‐light absorption properties of the flavoproteins.

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