This is the S systems model described in the article: Biochemical and genomic regulation of the trehalose cycle in yeast: review of observations and canonical model analysis Eberhard O Voit, J Theor Biol 2003 223:55-78 PubmedID: 12782117 ; DOI: 10.1016/S0022-5193(03)00072-9 Abstract: The physiological hallmark of heat-shock response in yeast is a rapid, enormous increase in the concentration of trehalose. Normally found in growing yeast cells and other organisms only as traces, trehalose becomes a crucial protector of proteins and membranes against a variety of stresses, including heat, cold, starvation, desiccation, osmotic or oxidative stress, and exposure to toxicants. Trehalose is produced from glucose 6-phosphate and uridine diphosphate glucose in a two-step process, and recycled to glucose by trehalases. Even though the trehalose cycle consists of only a few metabolites and enzymatic steps, its regulatory structure and operation are surprisingly complex. The article begins with a review of experimental observations on the regulation of the trehalose cycle in yeast and proposes a canonical model for its analysis. The first part of this analysis demonstrates the benefits of the various regulatory features by means of controlled comparisons with models of otherwise equivalent pathways lacking these features. The second part elucidates the significance of the expression pattern of the trehalose cycle genes in response to heat shock. Interestingly, the genes contributing to trehalose formation are up-regulated to very different degrees, and even the trehalose degrading trehalases show drastically increased activity during heat-shock response. Again using the method of controlled comparisons, the model provides rationale for the observed pattern of gene expression and reveals benefits of the counterintuitive trehalase up-regulation. To induce a heat shock, set the parameter heat_shock from 0 to 1. This changess the parameter values of X8 to X19 from 1 to the values given in table 3 of th eoriginal publication. As this is an S-systems model, it does not contain any reactions encoded in SBML.