FURTHER EXPERIMENTAL STUDIES ON THE HORSERADISH-PEROXIDASE OXIDASE REACTION

We study experimentally the changes in the kinetics and the thermodynamics for the periodically forced oxidation of reduced nicotinamide adenine dinucleotide (NADH) by molecular oxygen (referred to as the PO reaction), which is catalyzed by the horseradish peroxidase enzyme. We choose different forms of external periodic perturbations on the inflow of molecular oxygen to observe the effect of such forms on the dissipation and the efficiency of the system. On forcing an experimental limit cycle with a two-term Fourier series waveshape, we observe that the dissipation (efficiency) of the system is lowered (raised) relative to the autonomous system and that this change is related to the frequency of perturbation. Sinusoidal and nonsinusoidal perturbations of a stable focus in the experimental system also show that the dissipation is lowered relative to the autonomous state and that as the perturbation amplitude increases the dissipation decreases. Left-sawtooth perturbations are out-of-phase with the autonomous waveshape and on the stable focus lead to the lowest dissipation. Furthermore, the perturbation experiments on a stable focus indicate that NADH is a nonessential species in the PO reaction. Experimental evidence for quasiperiodicity in the PO reaction is presented for the first time. In the succeeding paper, we compare these experimental results with numerical results.