Metabolism of d -Arabinose: a New Pathway in Escherichia coli

Several growth characteristics of Escherichia coli K-12 suggest that growth on l -fucose results in the synthesis of all the enzymes necessary for growth on d -arabinose. Conversely, when a mutant of E. coli is grown on d -arabinose, all of the enzymes necessary for immediate growth on l -fucose are present. Three enzymes of the l -fucose pathway in E. coli , l -fucose isomerase, l -fuculokinase, and l -fuculose-l-phospháte aldolase possess activity on d -arabinose, d -ribulose, and d -ribulose-l-phosphate, respectively. The products of the aldolase, with d -ribulose-l-phosphate as substrate, are dihydroxyacetone phosphate and glycolaldehyde. l -Fucose, but not d -arabinose, is capable of inducing these activities in wild-type E. coli . In mutants capable of utilizing d -arabinose as sole source of carbon and energy, these activities are induced in the presence of d -arabinose and in the presence of l -fucose. Mutants unable to utilize l -fucose, selected from strains capable of growth on d -arabinose, are found to have lost the ability to grow on d -arabinose. Enzymatic analysis of cell-free extracts, prepared from cultures of these mutants, reveals that a deficiency in any of the l -fucose pathway enzymes results in the loss of ability to utilize d -arabinose. Thus, the pathway of d -arabinose catabolism in E. coli K-12 is believed to be: d -arabinose ⇌ d -ribulose → d -ribulose-l-phosphate ⇌ dihydroxyacetone phosphate plus glycolaldehyde. Evidence is presented which suggests that the glycolaldehyde is further oxidized to glycolate.