Stevens F J, Stevens P W, Hovis J G, Wu T T
J Gen Microbiol. 1981 May;124(1):219-23. doi: 10.1099/00221287-124-1-219.
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.
