Febs Letters Volume 51, Number 1./Volume 52, Number 1-2. [antikvár]

Volume 51, number 1 I'EBS LETTERS March 1975 PtsX: A GENE INVOLVED IN THE UPTAKE OF GLUCOSE AND FRUCTOSE BY ESCHERICHIA COLI H. L. KORNBERG and M. C. JONES-MORTIMER Department of Biochemistry, School of Biological Sciences. University of Leicester, Leicester LEI 7RH, England Received 14 January 1974 I. Introduction The uptalce by Escherichia eoli of a variety of carbohydrates necessarily involves the activity of a PEP-dependent phosphotransferase (FT) system [1 ], containing a number of components. Two of these, a small, histidine-containing protein (HPr) and an enzyme (Enzyme 1) that catalyses the transfer of phosphate from PEP to HPr, are required for the utiUzation of all carbohydrates that are taken up via the PT-system [2—6]. In contrast, the membrane-linked multicomponent fractions that effect the transfer of phosphate from the phosphorylated HPr to sugars (collectively termed Enzymes 11) are generally considered to be specific for individual sugars, although the uptake of any one sugar may involve the functioning of more than one Enzyme II. Thus, for example, the uptake by E. eoli of fructose at low concentration (< 2 mM) involves predominantly an Enzyme 11, specified by the ptsF gene (located at min. 41 on the L eoli genome) that catalyses the formation of fructose-1-phosphate, whereas at higlier concentrations (> 2 mM) fructose is phosphorylated also to fructose 6-phosphate by the action of a different Enzyme 11, specified by the ptsX gene (located at min. 35.5 on the E. eoli genome) [7-10]. It is the main purpose of this paper to present evidence that the Enzyme II specified by the ptsX gene is involved also in the uptake and phosphorylation of glucose. Mutants of E. eoli devoid of an Enzyme 11 that catalyses the phospliorylation of methyl-a-glucoside, specified by the un^g gene (located at min. 24 on the L¦. co/; genome, [11]), are markedly impaired in glucose utilization but still grow slowly on that sugar: we here show that umgptsX double mutants do not. It is thus likely that the ptsX marker corresponds to that designated gptB [12,13], which specifies a second Enzyme II for glucose and was first described by Curtis and Epstein [12]. 2. Experimental Cultures of E. eoli were grown, and their growth was measured, as previously described [14]. The incorporation of ['''C]glucose by cultures growing on a mixture of glucose and some other carbon source was determined as also previously described [15,16]. The genetical methods employed were those compiled by Miller [17]. Strains of E. eoli used are listed in table 1. 3. Results When cultures of E. eoli, grown either on sugars taken up via tlie PT-system (such as fructose) or on carbohydrates not taken up via that system (such as lactose) are suspended in growth media containing that carbon source and also containing glucose, the subsequent growth of the organisms occurs largely at the expense of the glucose. This preferential use of glucose is not seen with mutants that lack an Enzyme II for the uptake (and phosphorylation) of methyl-a-glucoside (and hence designated Umg") [15,16,18], which implies that the entry of glucose into the metabolic routes of E. eoli is effected largely via this Umg-system. This behaviour is illustrated in fig. I. A cuhure of strain K2.lt incorporated approx. 3 /tmol North-Holland Publishing Company - Amsterdam