CRYSTALLIZATION AND PROPERTIES OF L-ARABINOSE ISOMERASE FROM LACTOBACILLUS GAYONII

1. 1. l-Arabinose isomerase (l-arabinose ketol-isomerase, EC 5.3.1.4) was isolated in the crystalline state in 20% yield from the extracts of l-arabinose-grown cells of Lactobacillus gayonii. The molecular weight of the crystalline enzyme was estimated as 271 000 with the method of the sucrose density gradient centrifugation. 2. 2. The crystalline enzyme is specific for l-arabinose and l-ribulose. It is slightly active on d-galactose. The optimal pH for the isomerization of l-arabinose is 6.0-7.0, and the Michaelis constants are: 55 mM for l-arabinose and 5 mM for l-ribulose. 3. 3. The enzyme specifically requires Mn2+ for activity and the Michaelis constant is 5.25 μM. 4. 4. The enzyme activity is inhibited competitively by l-arabitol, ribitol or xylitol and the inhibition constants are: 7.5 mM for l-arbitol, 6 mM for ribitol and 38 mM for xylitol. © 1969.