title: Some properties of D-mannose isomerase from Escherichia coli K12.
abstract: A second-stage mutant of Escherichia coli K12 designated as strain 806 grew faster on D-lyxose than the mutant strain 805 previously described. Both mutants produced constitutively a novel enzyme, D-mannose isomerase, but strain 806 produced twice as much as strain 805. The enzyme could fortuitously convert D-lyxose to D-xylulose, which is a normal intermediate in the D-xylose catabolic pathway. The purified enzyme consisted of four subunits each with a molecular weight of about 40 000. In 0.14 M-Na2SO4, the tetramer dissociated completely into dimers. While the tetramer Km values for D-mannose and D-lyxose were 80 mM and 300 mM, respectively, the dimer Km values for these two sugars were both 300 mM. The amino acid composition of the enzyme was also determined.
mesh_terms: D019747:Aldose-Ketose Isomerases; D000596:Amino Acids / Q000032:analysis; D002238:Carbohydrate Epimerases / Q000302:isolation & purification; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D009154:Mutation; D012964:Sodium; D013379:Substrate Specificity; D013431:Sulfates
chemical_list: D000596:Amino Acids; D013431:Sulfates; C012036:sodium sulfate; D012964:Sodium; D002238:Carbohydrate Epimerases; D019747:Aldose-Ketose Isomerases; C032728:mannose isomerase