a simple self-maintaining metabolic system robustness, autocatalysis, bistability一个简单的自我维持的代谢系统健壮性、自动催化作用,双稳态.pdfVIP

A Simple Self-Maintaining Metabolic System: Robustness, Autocatalysis, Bistability 1 1 ´ 1 ´ ´ 2 2 Gabriel Piedrafita , Francisco Montero , Federico Moran , Marıa Luz Cardenas , Athel Cornish-Bowden * ´ ´ ´ ´ ´ ´ 1 Departamento de Bioquımica y Biologıa Molecular I, Facultad de Ciencias Quımicas, Universidad Complutense de Madrid, Madrid, Spain, 2 Bioenergetique et Ingenierie ´ des Proteines, Centre National de la Recherche Scientifique, Marseille, France Abstract A living organism must not only organize itself from within; it must also maintain its organization in the face of changes in its environment and degradation of its components. We show here that a simple (M,R)-system consisting of three interlocking catalytic cycles, with every catalyst produced by the system itself, can both establish a non-trivial steady state and maintain this despite continuous loss of the catalysts by irreversible degradation. As long as at least one catalyst is present at a sufficient concentration in the initial state, the others can be produced and maintained. The system shows bistability, because if the amount of catalyst in the initial state is insufficient to reach the non-trivial steady state the system collapses to a trivial steady state in which all fluxes are zero. It is also robust, because if one catalyst is catastrophically lost when the system is in steady state it can recreate the same state. There are three elementary flux modes, but none of them is an