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.

pH Wave-Front Propagation in the Urea-Urease Reaction

“…An early investigation focused on NADH and proton waves in yeast cell extracts (16). Fronts have also been observed in the hydrogenase-catalyzed oxidation of hydrogen (17) and with glucose oxidase (18). These systems have complicated kinetics involving multiple enzyme states.…”

Kinetics of the urea–urease clock reaction with urease immobilized in hydrogel beads

“…Although the reaction requires a single enzyme, the mechanism involves many radical reactions and multiple enzyme states with different oxidation states at the heme group active site. The hydrogenase enzyme catalyzed reaction also displays autocatalysis and propagating waves but the mechanism of this reaction is still under investigation [5].…”

Immobilization adjusted clock reaction in the urea–urease–H+ reaction system

“…There are a number of autocatalytic enzyme processes that produce both clocks and propagating fronts such as hydrogenase 22 or glucose oxidase. 23 Maintaining these features under immobilization conditions will allow for increased use of such nonlinear reactions.…”