Galactose Transport in Escherichia coli and the Galactose‐Binding Protein

Galactose uptake and galactose‐binding protein have been examined in a galactokinase‐deficient mutant of Escherichia coli K108.1 [ 14 C]Galactose was found to be accumulated up to one‐hundred‐thousand‐fold in the cytoplasm and to be subject to permanent turnover with unchanged velocity. 2 The concentration‐dependence curve exhibits sigmoïdicity and reveals a very high affinity of the system for galactose. The spectrum of specificity was explored by competition. 3 Metabolic inhibitors such as fluoride and uncouplers have weak or moderate effects, only a combination of several inhibitors can cause an efflux at a rate comparable to the rate of uptake. 4 Among inactivating agents N‐ethylmaleimide, parachloromercuribenzoate and dinitrofluorobenzene have no short term effects. Mercuric chloride and formaldehyde are strong inactivators. The effect of HgCl 2 is reversible by excess thiol. 5 Only small amounts of barium‐precipitable derivatives of galactose ( e.g. galactose 6‐phosphate) are observed and these do not exhibit turnover. 6 The concentrated shock fluid binds [ 14 C]galactose in equilibrium dialysis experiments. The binding curve is sigmoïdal with respect to galactose. 7 The binding is not abolished by HgCl 2 . The implications of these findings on possible transport mechanisms are discussed.