The role of electrostatic interactions in the formation of ferredoxin-ferredoxin NADP super(+) reductase and ferredoxin-hydrogenase complexes

A competitive Brownian model for the interaction of ferredoxin, ferredoxin NADP super(+) reductase and hydrogenase has been built. In the model, molecules of three types of proteins are placed into a cubic reaction volume, where they move under Brownian and electrostatic forces created by neighboring molecules and the solution. It has been shown that the rate of ferredoxin binding with ferredoxin NADP super(+) reductase does not change at the pH range from 5.0 to 9.0. Thus, it may be suggested that regulation of ferredoxin NADP super(+) reductase activity is mediated by other processes. On the other hand, the rate of ferredoxin binding with hydrogenase in the model depends greatly on pH: if the pH value increases from 6.0 to 8.0 the rate increases by factor of three. The increase of the pH value in the stroma under illumination results in an increase of the rate of its interaction with ferredoxin, but decreases the level of protons that are the substrate for the reaction catalyzed by the protein. Thus, the rate of hydrogen production in the chloroplast stroma is low at low pH due to the reception of a small number of electrons by hydrogenase. When the pH increases, the number of electrons that are received by the enzyme from ferredoxin also increases; thus, the rate of hydrogen production increases as well.