Abstract
Seventeen arabinose non-utilizing mutants of Escherichia coli strain B/r, previously ordered by genetic criteria and characterized by growth and accumulation experiments, have been defined enzymatically. Group A mutants are deficient in the enzyme L-arabinose isomerase and possess large amounts of L-ribulokinase, ranging from two to five times the activity shown by the wild type grown under similar conditions. Group B mutants are deficient in L-ribulokinase activity and have varying levels of L-arabinose isomerase activity, ranging from one-sixth to four times the wild type activity. Group C mutants are deficient in both isomerase and kinase activity. The grouping by enzymatic criteria corresponds exactly to the grouping by physiological and genetic criteria. Implications of the dual enzymatic effects in the various loci are discussed.