Ortega F, Acerenza L
Sección Biofisica, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay.
J Theor Biol. 1998 Apr 21;191(4):439-49. doi: 10.1006/jtbi.1997.0607.
In a previous work [Acerenza, L. (1993). Metabolic Control Design. J. theor. Biol. 165, 63-85] we devised a procedure to design metabolic systems that respond according to pre-established patterns. This procedure includes the mandatory structural and kinetic constraints that narrow the spectrum of responses. In an evolutionary context, the structural and functional features shown during the history of the system would also be conditioned by other factors. Here we incorporate to the Metabolic Control Design procedure two additional requirements that could have influenced metabolic evolution. These are constraints that result from the adaptation to the environment (represented by independent control coefficients that take fixed values) and optimization of metabolic variables at constant total enzyme concentration. To illustrate the general strategy we consider metabolic systems consisting of r reaction steps where the variables are the fluxes, internal metabolite concentrations, enzyme concentrations and control coefficients. In our conditions the number of degrees of freedom, calculated as number of variables minus number of number of relationships, is r - 1. A detailed analysis of three particular schemes, unbranched chain of two and three steps and branch point, with simple linear rate laws is given. Novel results are obtained for the optimization of the input flux of the simple branch point. In the well studied case where there are no evolutionary constraints one of the limbs of the branch point disappears. However, for particular independent control coefficients, when we impose to the control coefficient a fixed value, the branched structure may or may not persist depending on the range to which the fixed value belongs.
在之前的一项工作中[Acerenza, L. (1993). 代谢控制设计. 《理论生物学杂志》165, 63 - 85]，我们设计了一种程序来设计能根据预先设定模式做出响应的代谢系统。该程序包括强制性的结构和动力学约束，这些约束缩小了响应的范围。在进化背景下，系统历史中所呈现的结构和功能特征也会受到其他因素的制约。在此，我们将另外两个可能影响代谢进化的要求纳入到代谢控制设计程序中。这两个要求分别是对环境适应产生的约束（由取固定值的独立控制系数表示）以及在总酶浓度恒定的情况下对代谢变量的优化。为了阐述这一总体策略，我们考虑由r个反应步骤组成的代谢系统，其中变量包括通量、内部代谢物浓度、酶浓度和控制系数。在我们设定的条件下，自由度的数量通过变量数量减去关系数量来计算，结果为r - 1。我们对三种特定的方案进行了详细分析，即两步和三步的无分支链以及分支点，并采用了简单的线性速率定律。对于简单分支点的输入通量优化，我们获得了新的结果。在没有进化约束的充分研究案例中，分支点的一个分支会消失。然而，对于特定的独立控制系数，当我们给控制系数设定一个固定值时，分支结构可能会持续存在，也可能不会，这取决于该固定值所属的范围。
