On the active site of hydrogenase from Chromatium vinosum |
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Authors: | SPJ Albracht KJ Albrecht-Ellmer DJM Schmedding EC Slater |
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Institution: | Laboratory of Biochemistry, B.C.P. Jansen Institute, University of Amsterdam, P.O. Box 20151, 1000 HD Amsterdam The Netherlands |
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Abstract: | Isotope substitution of 57Fe () for 56Fe has a pronounced effect on the two EPR signals of hydrogenase of Chromatium vinosum. It is proposed that signal 1, the intensity of which is increased several-fold by a deoxygenation-oxygenation cycle with a simultaneous increase of a signal from Fe3+, is due to a 3Fe-xS] cluster. It is further proposed that signal 2 is caused by a magnetic interaction of a 4Fe-4S]3+ cluster with an unidentified paramagnet. The addition of 10 μM Ni to the culture medium (already containing 1 μM Ni) increased the enzyme activity 3–6-fold, without effect on the growth of the bacterium. Addition of 61Ni () to the medium did not change the EPR spectrum of hydrogenase. From a comparison of the EPR signal intensities and the enzyme activities it is concluded that, in the hydrogenase preparation as isolated, molecules containing a 3Fe-xS) cluster are not active, and that active molecules have a 4Fe-4S]3+(3+,2+) cluster plus an as yet unidentified paramagnetic redox component. The latter is thought to be the primary site of interaction of the enzyme with H2. Ni is considered as a possible candidate for this component. |
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Keywords: | Hydrogenase ESR Nickel Iron-sulfur protein Active site (C vinosum) |
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