THE PEROXIDASE-OXIDASE REACTION: A CASE FOR CHAOS IN THE BIOCHEMISTRY OF THE CELL

Biochemists generally assume that the metabolic state of the cell is a stable steady state, although they also acknowledge that such a steady state may change with time. However, in early 1976 Otto Rössler demonstrated that simple models of chemical and biochemical reactions may exhibit dynamics in which metabolites fluctuate wildly in time in an apparently random fashion with no recurrency. Similar behavior was reported a decade earlier by Edward Lorenz in his studies of a simple model of the weather. Chaos as this irregular behavior was coined soon became a popular research topic in almost all scientific disciplines. Shortly after its discovery in chemical models, chaos was observed experimentally in both biochemical and chemical reactions. The peroxidase–oxidase reaction, in which reduced nicotinamide adenine dinucleotide (NADH) is oxidised by molecular oxygen, was the first biochemical system to exhibit chaotic behavior. Although only a single enzyme, peroxidase, is involved, the reaction has similar regulatory properties as many biochemical pathways, which involve many enzymes, and hence it may be considered as a simple model of cell metabolism. We describe a few of the many dynamic behaviors found experimentally and in models of the peroxidase–oxidase reaction. On the basis of these observations we propose that a stable steady state is the least likely dynamic possibility of cell metabolism …