The enzyme 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (DAH7PS) catalyses the reaction between erythrose 4-phosphate and phosphoenolpyruvate. DAH7PS is the enzyme responsible for the first committed step in the shikimate pathway, toward the formation of aromatic compounds, including the aromatic amino acids. This pathway and DAH7PS are only present in plants and microorganisms, and thus potential drug targets. There are three different types of DAH7PS which are characterised by additions to the core TIM-barrel structure and these extensions are associated with the allosteric regulation of the enzyme. Pyrococcus furiosus DAH7PS (PfuDAH7PS) is one of the simplest DAH7PSs structurally, with no modifications adorning the core barrel structure, and as such, is not feedback regulated. Like many other DAH7PS enzymes, PfuDAH7PS is observed in crystal structures as a tetramer but whether the dimer or tetramer is the biologically active species has been the subject of debate. In this work, the importance of the quaternary structure and the relationship between the structure, function and stability of this enzyme has been studied. Analytical ultracentrifugation and small angle X-ray scattering were used to investigate the quaternary structure of PfuDAH7PS in solution. Results indicate that a single mutation in the dimer-dimer interface of PfuDAH7PS is sufficient to disrupt the tetrameric structure of the enzyme and an equilibrium exists between the dimeric and tetrameric states of the variant enzyme.