An autocatalytic step in the reaction cycle of hydrogenase
from Thiocapsa roseopersicina can explain the
special characteristics of the enzyme reaction
Judit sz 1 and Csaba Bagyinka 1*
1 Institute of Biophysics, Biological Research Center, Szeged, Hungary
* To whom correspondence should be addressed. E-mail: csaba{at}nucleus.szbk.u-szeged.hu.
Submitted on January 8, 2005
Revised on February 21, 2005
Accepted on 31 May 2005
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Abstract |
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A moving front has been observed as a special pattern during the hydrogenase-catalyzed reaction of hydrogen uptake with benzyl viologen as electron acceptor in a thin-layer reaction chamber. Such fronts start spontaneously and at random times at different points of the reaction chamber; blue spheres are seen expanding at constant speed and amplitude. The number of observable starting points depends on the hydrogenase concentration. Fronts can be initiated by injecting either a small amount of completed reaction mixture or activated hydrogenase, but not by injecting a low concentration of reduced benzyl viologen. These characteristics are consistent with an autocatalytic reaction step in the enzyme reaction. The special characteristics of the hydrogen-uptake reaction in the bulk reaction (a long lag phase, and the enzyme concentration dependence of the lag phase) support the autocatalytic nature. We conclude that there is at least one autocatalytic reaction step in the hydrogenase-catalyzed reaction. The two possible autocatalytic schemes for hydrogenase are prion-type autocatalysis, in which two enzyme forms interact, and product-activation autocatalysis, where a reduced electron acceptor and an inactive enzyme form interact. The experimental results strongly support the occurrence of prion-type autocatalysis.
Key Words:
autocatalytic, enzyme reaction, hydrogenase, wavefront
