The in vivo distribution of metabolic fluxes in Escherichia coli can
be predicted from optimality principles At least two different sets of optimality principles govern the
operation of the metabolic network under different environmental
conditionsMetabolism during unlimited growth on glucose in batch culture is
best described by the nonlinear maximization of ATP yield per unit of
flux
Although the network topology of metabolism is well known, understanding the principles that govern the distribution of fluxes through metabolism lags behind. Experimentally, these fluxes can be measured by (13)C-flux analysis, and there has been a long-standing interest in understanding this functional network operation from an evolutionary perspective. On the basis of (13)C-determined fluxes from nine bacteria and multi-objective optimization theory, we show that metabolism operates close to the Pareto-optimal surface of a three-dimensional space defined by competing objectives. Consistent with flux data from evolved Escherichia coli, we propose that flux states evolve under the trade-off between two principles: optimality under one given condition and minimal adjustment between conditions. These principles form the forces by which evolution shapes metabolic fluxes in microorganisms' environmental context.
Six symmetrical tetrachlorobiphenyls have been synthesized. Cyclohexane and methanol solutions of I-VI were irradiated at 300 nm and the products of the reaction identified. In both solvents dechlorination is the major reaction. Intersystem crossing quantum yields and quantum yields of reaction for I-VI have been determined in solution. The excited state responsible for photoreaction was found to be the triplet, and its lifetime was measured in cyclohexane and methanol. The rate constants for triplet decay and reaction were obtained using these data. The position of chloro substitution was found to have a marked effect on the photochemical properties of polychlorobiphenyls; an increase in ortho substituents decreased the lifetime and increased the reactivity of the excited state.
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