Figure 1

A segment of a model metabolic pathway. This diagram shows those features, discussed in the text, that permit a systemic analysis of the response of any variable of a metabolic system (e.g. a flux J or the concentration of any intracellular metabolite S) to changes in any one parameter of the system (e.g. an enzyme activity). Each S is an intracellular metabolite; each X is an extracellular metabolite. In a diploid cell, every E stands for a pair of enzymes (allozymes), each specified by one of the two alleles at a gene locus. Each E is then a locus of catalytic activity within a system of enzymes; each v stands for the individual reaction rates catalysed jointly by a pair of allozymes in a diploid cell. Either or both allozymes at such a locus may be mutated.