Glucose Effect in tgl Mutant of Escherichia coli K12 Defective in Methyl‐α‐D‐glucoside Transport

Abstract

1. The dependence of the rate of accumulation of methyl-a-D-glucoside on its extracellular concentration was studied in the tglmutant of Escherichia coli K12, isolated earlier. It has been shown that the kinetics of methyl-a-D-glucoside transport differ sharply from those in wild-type bacteria.2. The /3-galactosidase synthesis in tgl strain is much less sensitive both to permanent and transient glucose catabolite repression. The level of cyclic AMP in mutant cells under the conditions of glucose catabolite repression is several times higher than in the parent strain.3. The tgf mutation does not affect the manifestation of catabolite inhibition and inducer exclusion with glucose.4. The data obtained are discussed in the light of a hypothesis concerning the existence of two sites, binding and phosphorylating, in the molecule of the glucose (and methyl-cr-D-glucoside) specific enzyme I1 of the phosphoenolpyruvate-dependent phosphotransferase system. The tgl mutation alters the first site, and the second one is damaged by the gpt mutation.5. It is suggested that the products of the tgl and gpt genes are necessary for the manifestation of the phenomena of glucose permanent and transient repression. The effects of catabolite inhibition and inducer exclusion are realized irrespective of the existence or absence of the tgl product.

Defective enzyme II-BGlc of the phosphoenolpyruvate:sugar phosphotransferase system leading to uncoupling of transport and phosphorylation in Salmonella typhimurium

“…In those cases, phosphorylation and transport of glucose, catalyzed by II-BGlc, are completely absent, even at high external concentrations. The pts-418 mutation is also different from the tgl mutation described by Gershanovitch and coworkers in E. coli (1,5). tgl mutants are still able to phosphorylate methyl a-glucoside, provided it can reach its phosphorylation site inside the cell.…”

“…Enzyme II-B('c could be composed of more than one subunit. ptsG might code for a protein that is involved in methyl a-glucoside phosphorylation, whereas a second gene might code for a protein which is responsible for transport per se (1,5,6). If those two genes are closely linked, introduction of the ptsG: :TnlO mutation would at the same time eliminate also the pts-418 mutation, which is responsible for the transport of glucose in AptsHI galP strains.…”

Enzymes II of the phosphotransferase system do not catalyze sugar transport in the absence of phosphorylation

“…Mutational events could possibly lead to altered enzymes II with dissociated phosphorylation and transport activities. For instance, Bourd et al and Erlagaeva et al (2,4) and Kornberg and Jones-Mortimer (8) have described mutations in E. coli, designated tgl, which impair methyl a-glucoside transport but allow normal phosphorylation of this sugar in sonic extracts or in cells made permeable by toluene treatment. On the other hand, we have described mutants of S. typhimurium in which the enzyme II specific for mannose and glucose may catalyze the facilitated diffusion of galactose in the absence of phosphorylation (15).…”

Fructose-specific phosphoenolpyruvate dependent phosphotransferase system of Escherichia coli: Its alterations and adenylate cyclase activity

“…The fruA mutation effect on AC activity is of interest. Mutations of ptsG or tgl are known to damage the glucose specific enzymeII activity and to result in activation of AC, hence the increase of cAMP intercellular content [27]. In the case of EllCru, however, an opposite situation occurs.…”