Abstract
D-Arabinose(L-fucose) isomerase (D-arabinose ketol-isomerase, EC 5. 3. 1. 3) was purified from the extracts of D-arabinose-grown cells of Aerobacter aerogenes, strain M-7 by the procedure of repeated fractional precipitation with polyethylene glycol 6000 and isolating the crystalline state. The crystalline enzyme was homogeneous in ultracentrifugal analysis and polyacrylamide gel electrophoresis. Sedimentation constant obtained was 15.4s and the molecular weight was estimated as being approximately 2.5×105 by gel filtration on Sephadex G-200.
Optimum pH for isomerization of D-arabinose and of L-fucose was identical at pH 9.3, and the Michaelis constants were 51 mM for L-fucose and 160mM for D-arabinose. Both of these activities decreased at the same rate with thermal inactivation at 45 and 50°C. All four pentitols inhibited two pentose isomerase activities competitively with same Ki values: 1.3-1.5mM for D-arabitol, 2.2-2.7mM for ribitol, 2.9-3.2mM for L-arabitol, and 10-10.5mM for xylitol. It is confirmed that the single enzyme is responsible for the isomerization of D-arabinose and L-fucose.
