The gene-protein-reaction relationship. Boolean logic is used to describe gene-protein-reaction (GPR) relationships of varying complexity. Reactions can carry flux if and only if a correct combination of genes is expressed. Reaction 1 is catalyzed by a single gene product (reaction 1 ⇔ gene a). Reactions 2 and 3 are both catalyzed by the product of gene b (reaction 1 ⇔ gene b, reaction 2 ⇔ gene b). Genes c and d produce subunits of an enzymatic complex; both proteins are required for reaction 4 to carry flux (reaction 4 ⇔ gene c andgene d). Genes e and f encode isozymes. Either enzyme can catalyze reaction 5 (reaction 5 ⇔ gene e or gene f ).
Jensen et al. BMC Systems Biology 2011 5:147 doi:10.1186/1752-0509-5-147