The D-ribulokinase and D-xylulokinase of Klebsiella aerogenes were purified to homogeneity from Escherichia coli K12 construct strains that synthesized these enzymes constitutively. The D-ribulokinase, which is encoded in the ribitol operon, is active as a dimer of 60 000 subunit mol.wt., whereas the D-xylulokinase, which is encoded in the D-arabitol operon, is active as a dimer of 54 000 subunit mol.wt. The amino acid compositions and N-terminal sequences of both pentulokinases are reported. The Kapp. values of the enzymes for their D-pentulose substrates were determined, and the D-ribulokinase was shown to have a low-affinity side-specificity for ribitol and D-arabitol. These results are discussed in the context of the evolution of the Klebsiella aerogenes pentitol operons.
