Crystalline cross-linked xylose isomerase (CLXI, EC 5.3.1.5) and xylanase (CLX, EC 3.2.1.8) were studied in a packed-bed reactor for simultaneous catalytic reaction and separation of substrates from reaction products. Streptomyces rubiginosus xylose isomerase catalyzed a slow isomerization of L-arabinose to L-ribulose and an epimerization to L-ribose. In equilibrium the reaction mixture contained 52.5% arabinose, 22.5% ribulose, and 25% ribose. In a packed-bed column filled with CLXI, a simultaneous reaction and separation resulted in fractions where arabinose concentration varied between 100-0%, ribulose between 0-55%, and ribose between 0-100%. Trichoderma ressei xylanase II hydrolyzed and transferred xylotetraose mainly to xylotriose and xylobiose. In a packed-bed column filled with CLX, xylotetraose rapidly reacted to xylobiose and xylose by a mechanism that is not yet fully understood. (C) 2001 John Wiley & Sons, Inc.