Abstract
Three mutations clustered at 45.5 min of the genetic map of E. coli K12 have been shown previously (Lengeler, 1975a) to affect specifically galactitol transport via an enzyme II-complexGat (gatA) of the PEP dependent phosphotransferase system and a soluble, NAD dependent dehydrogenase (gatD). In the present report data are given further supporting the existence of a gat operon, made up by a control gene gatC and the structural genes gatA and gatD. The enzyme II-complexGat is shown to catalyze the formation of galactitol-1-P and the dehydrogenase to catalyze the reversible conversion of galactitol-1-P and D-tagatose-6-P. Loss of a phosphofructokinase activity controlled by the gene pfkA prevents growth on galactitol and concomitantly the formation of D-tagatose-1,6-P2, while the suppressing mutation pfkB-1 restores a phosphofrucokinase activity and growth on galactitol.
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