Indexed on: 24 May '11Published on: 24 May '11Published in: Enzyme research
Dehydroquinate synthase (DHQS) catalyses the second step of the shikimate pathway to aromatic compounds. DHQS from the archaeal hyperthermophile Pyrococcus furiosus was insoluble when expressed in Escherichia coli but was partially solubilised when KCl was included in the cell lysis buffer. A purification procedure was developed, involving lysis by sonication at 30°C followed by a heat treatment at 70°C and anion exchange chromatography. Purified recombinant P. furiosus DHQS is a dimer with a subunit Mr of 37,397 (determined by electrospray ionisation mass spectrometry) and is active over broad pH and temperature ranges. The kinetic parameters are K(M) (3-deoxy-D-arabino-heptulosonate 7-phosphate) 3.7 μM and k(cat) 3.0 sec(-1) at 60°C and pH 6.8. EDTA inactivates the enzyme, and enzyme activity is restored by several divalent metal ions including (in order of decreasing effectiveness) Cd(2+), Co(2+), Zn(2+), and Mn(2+). High activity of a DHQS in the presence of Cd(2+) has not been reported for enzymes from other sources, and may be related to the bioavailability of Cd(2+) for P. furiosus. This study is the first biochemical characterisation of a DHQS from a thermophilic source. Furthermore, the characterisation of this hyperthermophilic enzyme was carried out at elevated temperatures using an enzyme-coupled assay.