Metabolism of d -Arabinose by Aerobacter aerogenes : Purification of the Isomerase a

Abstract

In Aerobacter aerogenes , the mutational event permitting the utilization of d -arabinose as a source of carbon and energy is a regulatory mutation resulting in the constitutive synthesis of certain enzymes of the l -fucose catabolic pathway. l -Fucose isomerase catalyzes the isomerization of d -arabinose to d -ribulose. This enzyme was purified to homogeneity as indicated by a single band in disc-gel electrophoretic columns and single peaks with column chromatography and ultracentrifugation from the wild-type PRL-R3 strain, induced with l -fucose and two constitutive mutants, 502 and 510. The ratios of the activities of this isomerase on d -arabinose and l -fucose remained constant throughout all purifications. The apparent K _m of the isomerase from the wild-type strain induced with l -fucose and from the constitutive mutant strains was 5.0 × 10 ⁻² m for l -fucose and 1.5 × 10 ⁻¹ m for d -arabinose. A strain 531 possessing an apparent alteration in the isomerase was isolated from the strain 502. This altered isomerase exhibited a lowered K _m for d -arabinose.