Properties of d-Arabinose Isomerase Purified from Two Strains of Escherichia coli
Journal of Bacteriology
D-Arabinose isomerase (EC 18.104.22.168) has been isolated from L-fucose-induced cultures of Escherichia coli K-12 and D-arabinose-induced cultures of E. coli B/r. Both enzymes were homogeneous in an ultracentrifuge and migrated as single bands upon disc electrophoresis in acrylamide gels. The s20.w was 14.5 x 10-13 sec for the E. coli K-12 enzyme and 14.3 x 10-13 sec for the E. coli B/r enzyme. The molecular weight, determined by high-speed sedimentation equilibrium, was 3.55 a 0.06 x 106 for the E.
... 06 x 106 for the E. coli K-12 enzyme and 3.42 0.04 x 106 for the enzyme isolated from E. coli B/r. Both enzyme preparations were active with L-fucose or D-arabinose as substrates and showed no activity on any of the other aldopentoses or aldohexoses tested. With the E. coli K-12 enzyme, Although it is able to utilize L-fucose, wildtype E. coli K-12 is unable to utilize Darabinose as a sole source of carbon and energy. Recent work by LeBlanc and Mortlock (6) has shown that growth on L-fucose of an E. coli K-12 strain, selected for its ability to grow on D-arabinose, results in the synthesis of the enzymes necessary for growth on D-arabinose. They suggest that the L-fucose isomerase is responsible for the isomerization of D-arabinose to D-ribulose in this organism. E. coli B/r is able to utilize the pentose D-arabinose as a sole source of carbon and energy. This strain will grow on D-arabinose with a doubling time of 120 min, but cannot metabolize L-fucose. In E. coli B/r, both D-687 on May 9, 2020 by guest