Autocatalytic, bistable, oscillatory networks of biologically relevant organic reactions

A few-component network of biologically relevant, organic reactions displays bistability and oscillations, without an enzymatic catalyst. Oscillatory reactions in a simple organic system Dissipative chemical reaction networks are systems that operate away from equilibrium and exhibit features such as continuous regeneration of components and autonomous regulation. The biological cell is one such out-of-equilibrium chemical network. Until now it has not been possible to recreate this type of dynamic behavior using simple organic molecules relevant to prebiotic Earth. Now, George Whitesides and colleagues demonstrate a few-component system of interacting organic species that, combined into a reaction network, displays autocatalytic and oscillatory features. All of the organic components are relatively simple and do not require enzymatic catalysis to react. Networks of organic chemical reactions are important in life and probably played a central part in its origin 1 , 2 , 3 . Network dynamics regulate cell division 4 , 5 , 6 , circadian rhythms 7 , nerve impulses 8 and chemotaxis 9 , and guide the development of organisms 10 . Although out-of-equilibrium networks of chemical reactions have the potential to display emergent network dynamics 11 such as spontaneous pattern formation, bistability and periodic oscillations 12 , 13 , 14 , the principles that enable networks of organic reactions to develop complex behaviours are incompletely understood. Here we describe a network of biologically relevant organic reactions (amide formation, thiolate–thioester exchange, thiolate–disulfide interchange and conjugate addition) that displays bistability and oscillations in the concentrations of organic thiols and amides. Oscillations arise from the interaction between three subcomponents of the network: an autocatalytic cycle that generates thiols and amides from thioesters and dialkyl disulfides; a trigger that controls autocatalytic growth; and inhibitory processes that remove activating thiol species that are produced during the autocatalytic cycle. In contrast to previous studies that have demonstrated oscillations and bistability using highly evolved biomolecules (enzymes 15 and DNA 16 , 17 ) or inorganic molecules of questionable biochemical relevance (for example, those used in Belousov–Zhabotinskii-type reactions) 18 , 19 , the organic molecules we use are relevant to metabolism and similar to those that might have existed on the early Earth. By using small organ