RT Journal Article SR Electronic(1) A1 Lehmacher, Anselm A1 Bisswanger, HansYR 1990 T1 Isolation and characterization of an extremely thermostable D-xylose isomerase from Thermus aquaticus HB 8 JF Microbiology, VO 136 IS 4 SP 679 OP 686 DO https://doi.org/10.1099/00221287-136-4-679 PB Microbiology Society, SN 1465-2080, AB The extremely thermophilic organism Thermus aquaticus possesses high activities of enzymes catalysing the degradation of xylans and metabolizing d-xylose via the pentose phosphate pathway. The d-xylose isomerase (d-xylose ketol-isomerase, EC 5.3.1.5), an important enzyme of this process, is efficiently induced by its substrate d-xylose, and, to a lesser extent, by related pentoses and some derivatives of d-xylose. The d-xylose isomerase from T. aquaticus has been purified by anion-exchange chromatography, chromatography on d-xylose agarose and gel filtration. A single band migrating according to an M r of 50000 was obtained by SDS-PAGE. An M r of 196000 for the native enzyme, determined by gel filtration and ultracentrifugation in a glycerol gradient, suggested that the d-xylose isomerase is a homomeric tetramer. Arrhenius plots of the enzyme activity of the d-xylose isomerase were linear up to a temperature of 85 °C. At 70 °C the enzyme was inactivated in the absence of divalent cations, with a half-life of 4 d, while in the presence of Mn2+ or Co2+ it remained fully active for at least 1 month. The enzyme had an isoelectric point at 4·4 and showed a broad optimum in the pH range from 5·5 to 8·5. No significant differences in the pH and temperature behaviour could be observed when d-xylose was compared with d-glucose as substrate. Different methods of immobilization of the enzyme to solid supports as well as inclusion into nylon beads were studied. Attachment of the enzyme to epoxy-activated agarose and its co-aggregation with bovine serum albumin gave immobilized preparations with the same stability as free enzyme supplemented with Mn2+ or Co2+., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-136-4-679