D-Glucose isomerase: constitutive and catabolite repression-resistant mutants of Streptomyces phaeochromogenes.

As in other Streptomyces species, the enzymatic conversion of D-glucose to D-fructose is carried out in Streptomyces phaeochromogenes NRRL B-3559 by the inducible enzyme, D-xylose keto isomerase (EC 5.3.1.5). Mutants of this microorganism were selected for their ability to grow on D-lyxose (2-epimer of D-xlose). As a result of the mutational event, the microorganism constitutively produced D-xylose isomerase. As in the parent strain, the constitutive formation of the isomerase was repressed by D-glucose. The fact that this mutant was unable to grow in low D-xylose concentrations in the presence of the D-glucose analogue, 3-O-methylglucose, permitted the isolation of D-xylose isomerase constitutive mutants which were insensitive to D-glucose repression.