The Pyrococcus horikoshii OT3 genome contains a gene encoding a human kynurenine aminotransferase II (KAT II) homologue, which consists of 428 amino-acid residues and shows an amino-acid sequence identity of 30% to human KAT II. This gene was overexpressed in Escherichia coli and the recombinant protein (Ph-KAT II) was purified. Gel-filtration chromatography showed that Ph-KAT II exists as a homodimer. Ph-KAT II exhibited enzymatic activity that catalyzes the transamination of L-kynurenine to produce kynurenic acid. Crystals of Ph-KAT II were grown using the sitting-drop vapour-diffusion method and native X-ray diffraction data were collected to 2.2 A resolution using synchrotron radiation from station BL44XU at SPring-8. The crystals belong to the centred orthorhombic space group C222(1), with unit-cell parameters a = 71.75, b = 86.84, c = 137.30 A. Assuming one molecule per asymmetric unit, the VM value was 2.19 A3 Da(-1) and the solvent content was 43.3%.
