L-Sorbose phosphorylation in Escherichia coli K-12

L-Sorbose is phosphorylated by Escherichia coli by two distinct Enzymes II of the phosphoenolpyruvate-dependent phosphotransferase system. The glucose Enzyme II (specified by the gene ptsG) phosphorylates L-sorbose with an apparent Km of 0.08 +/- 0.03 mM and V of 31.8 +/- 3.5 nmol . mg-1 . min-1 whilst the fructose Enzyme II (specified by the gene ptsF) phosphorylates it with an apparent Km of 28.9 +/- 2.7 mM and V of 20.2 +/- 0.8 nmol . mg-1 . min-1. L-Sorbose induces neither of these Enzymes II, but sorbose inhibits the growth of strains expressing either of these functions constitutively. Mutants that have lost their sensitivity to L-sorbose are found to have lost either the glucose or the fructose phosphotransferase Enzyme II.U