E. coli K12 cannot grow on D lyxose, but a mutant was isolated which can utilize D lyxose as sole source of carbon and energy for growth. D Lyxose is transported into the bacteria by the D xylose permease. The mutant constitutively synthesizes a new isomerase which is not inducible in the parent strain under any of the conditions tested. This enzyme, whose native substrate appears to be D mannose, fortuitously converts D lyxose into D xylulose. Its structural gene is located at around 85 min on the E. coli genetic map, away from other known isomerase genes. D Xylulose is subsequently catabolized by the enzymes of the normal D xylose metabolic pathway. D Mannose isomerase was partially purified and some of its properties were examined.
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