title: Concentration-dependent front velocity of the autocatalytic hydrogenase reaction.
abstract: HynSL hydrogenase from Thiocapsa roseopersicina was applied to catalyze the oxidation of molecular hydrogen in a new, improved, thin-layer reaction chamber. Investigation of the nature of this catalysis via the development of reduced benzyl viologen showed clearly the typical characteristics of an autocatalytic reaction: propagation of a reaction front originating from a single point, with a constant velocity of front propagation. The dependence of the reaction velocity on enzyme concentration was a power function with a positive enzyme concentration threshold, with an exponent of 0.4 +/- 0.05. This indicates that the autocatalyst is an enzyme form. The front velocity decreased on increase of the electron acceptor concentration, as a sign that the autocatalyst interacts directly with the final electron acceptor. Overall, it may be concluded that the autocatalyst is an enzyme form in which [FeS]distal is reduced. Model calculations corroborate this. Because the reduction of all [FeS] clusters would be possible in a nonautocatalytic reaction, we hypothesize a small conformational change in the enzyme, catalyzed by the autocatalyst, which removes a block in the electron flow in either [NiFe] --> [FeS]proximal or the [FeS]proximal --> [FeS]distal reaction step, or removes a block of the penetration of gaseous hydrogen from the surface to the [NiFe] cluster.
authors.affiliation: Institute of Biophysics, Biological Research Center, Szeged, H-6726, Hungary.
authors.forename: Gabriella
authors.initials: G
authors.lastname: Bodó
authors.forename: Rui M M
authors.initials: RM
authors.lastname: Branca
authors.forename: Agota
authors.initials: A
authors.lastname: Tóth
authors.forename: Dezsó
authors.initials: D
authors.lastname: Horváth
authors.forename: Csaba
authors.initials: C
authors.lastname: Bagyinka
mesh_terms: D055162:Biocatalysis; D004579:Electron Transport; D006859:Hydrogen / Q000378:metabolism; D006864:Hydrogenase / Q000737:chemistry* / Q000378:metabolism*; D008954:Models, Biological; D010084:Oxidation-Reduction; D020616:Thiocapsa roseopersicina / Q000201:enzymology*
chemical_list: D006859:Hydrogen; D006864:Hydrogenase