Diagrammatic approach to calculation of the fluctuation correlation matrixin a metabolic system

We present here a simple diagrammatic approach for the time evolution of th e fluctuations in metabolite concentrations around the steady state. A fluc tuation correlation matrix is introduced to characterise the response in th e concentrations of metabolites to a singular initial fluctuation in one of the metabolites. We show how the temporal evolution of the correlation mat rix can be represented in the form of a series with individual terms corres ponding to pathways on a metabolic graph. The basic properties of such grap hs are studied and it is shown how each term in the series can be evaluated . A Monte-Carlo procedure is outlined to calculate the fluctuation correlat ion matrix. We discuss various properties of the graphical representation a nd discuss links to information theory that arise from it. (C) 2000 Elsevie r Science Ireland Ltd. All rights reserved.