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Water Relaxation Measurements on Semiquinones of Various Flavoproteins
Author(s) -
Visser Antonie J. W. G.,
De Wit Jan L.,
Müller Franz,
Berendsen Herman J. C.
Publication year - 1982
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19820650807
Subject(s) - chemistry , flavodoxin , flavoprotein , semiquinone , relaxation (psychology) , azotobacter vinelandii , proton , reaction rate constant , ionic bonding , kinetics , inorganic chemistry , nitrogenase , biochemistry , ion , nitrogen , enzyme , social psychology , psychology , redox , ferredoxin , physics , quantum mechanics , nitrogen fixation , organic chemistry
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.