Carbohydrate transport in bacteria

Involvement of lactose enzyme II of the phosphotransferase system in rapid expulsion of free galactosides from Streptococcus pyogenes

Streptococcus pyogenes accumulated thiomethyl-beta-galactoside as the 6-phosphate ester due to the action of the phosphoenolpyruvate:lactose phosphotransferase system. Subsequent addition of glucose resulted in rapid efflux of the free galactoside after intracellular dephosphorylation (inducer expulsion). Efflux was shown to occur in the apparent absence of the galactose permease, but was inhibited by substrate analogs of the lactose enzyme II and could not be demonstrated in a mutant of S. lactis ML3 which lacked this enzyme. The results suggest that the enzymes II of the phosphotransferase system can catalyze the rapid efflux of free sugar under appropriate physiological conditions.

Intracellular hexose-6-phosphate:phosphohydrolase from Streptococcus lactis: purification, properties, and function

An intracellular hexose 6-phosphate:phosphohydrolase (EC 3.1.3.2) has been purified from Streptococcus lactis K1. Polyacrylamide disc gel electrophoresis of the purified enzyme revealed one major activity staining protein and one minor inactive band. The Mr determined by gel permeation chromatography was 36,500, but sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a single polypeptide of apparent Mr 60,000. The enzyme exhibited a marked preference for hexose 6-phosphates, and the rate of substrate hydrolysis (at 5 mM concentration) decreased in the order, galactose 6-phosphate greater than 2-deoxy-D-glucose 6-phosphate greater than fructose 6-phosphate greater than mannose 6-phosphate greater than glucose 6-phosphate. Hexose 1-phosphates, p-nitrophenylphosphate, pyrophosphate, and nucleotides were not hydrolyzed at a significant rate. In addition, the glycolytic intermediates comprising the intracellular phosphoenolpyruvate potential in the starved cells (phosphoenolpyruvate and 2- and 3-phosphoglyceric acids) were not substrates for the phosphatase. Throughout the isolation, the hexose 6-phosphate:phosphohydrolase was stabilized by Mn2+ ion, and the purified enzyme was dependent upon Mn2+, Mg2+, Fe2+, or Co2+ for activation. Other divalent metal ions including Pb2+, Cu2+, Zn2+, Cd2+, Ca2+, Ba2+, Sr2+, and Ni2+ were unable to activate the enzyme, and the first four cations were potent inhibitors. Enzymatic hydrolysis of 2-deoxy-D-glucose 6-phosphate was inhibited by fluoride when Mg2+ was included in the assay, but only slight inhibition occurred in the presence of Mn2+, Fe2+, or Co2+. The inhibitory effect of Mg2+ plus fluoride was specifically and completely reversed by Fe2+ ion. The hexose 6-phosphate:phosphohydrolase catalyzes the in vivo hydrolysis of 2-deoxy-D-glucose 6-phosphate in stage II of the phosphoenolpyruvate-dependent futile cycle in S. lactis (J. Thompson and B. M. Chassy, J. Bacteriol. 151:1454-1465, 1982).

Molecular cloning of the uhp region and evidence for a positive activator for expression of the hexose phosphate transport system of Escherichia coli

The uhp locus of Escherichia coli contains genes for the sugar phosphate transport system (uhpT) and the regulatory system which allows its induction by external glucose 6-phosphate (uhpRA). The uhp region was cloned onto high-copy-number plasmids, both from Uhp(+) plasmids of the Clarke-Carbon collection and from genetically characterized specialized transducing phages carrying uhpT-lac operon fusions. Two Clarke-Carbon plasmids and their Uhp(+) subclones in pBR322 shared restriction sites defining the uhp region, but exhibited different regulation of Uhp expression and dependence on chromosomal uhp genotype. Plasmid pLC17-47 and derivatives conferred constitutive glucose 6-phosphate uptake activity in all strains, even those with complete deletions of uhp. These plasmids also rendered constitutive the expression of a chromosomal uhpT-lac operon fusion. Plasmid pLC40-33 conferred inducible Uhp expression, which required the presence of the uhpA(+) gene on the chromosome. The induced transport levels in all strains carrying these plasmids were not appreciably amplified over haploid levels. Similar behavior was seen with the cloned operon fusions. A fusion-bearing plasmid that carried an intact regulatory system (uhpR(+)A(+)) exhibited trans-dominant constitutive expression of beta-galactosidase, regardless of the chromosomal uhp genotype. In contrast, the cloned fusion carrying only uhpR(+) gave glucose 6-phosphate-inducible production of beta-galactosidase that was dependent on the presence of chromosomal uhpA(+). Expression of both fusions in the haploid state was inducible. From these results, it was concluded that the uhpA product is necessary for uhpT transcription and that elevated dosage of uhpA results in at least partially constitutive expression of uhpT. A tentative model for uhp regulation is presented.

Cooperative binding of the sugar substrates and allosteric regulatory protein (enzyme IIIGlc of the phosphotransferase system) to the lactose and melibiose permeases in Escherichia coli and Salmonella typhimurium

An Escherichia coli strain which overproduces the lactose permease was used to investigate the mechanism of allosteric regulation of this permease and those specific for melibiose, glycerol, and maltose by the phosphoenolpyruvate-sugar phosphotransferase system (PTS). Thio-beta-digalactoside, a high affinity substrate of the lactose permease, released the glycerol and maltose permeases from inhibition by methyl-alpha-d-glucoside. Resumption of glycerol uptake occurred immediately upon addition of the galactoside. The effect was not observed in a strain which lacked or contained normal levels of the lactose permease, but growth of wild-type E. coli in the presence of isopropyl-beta-thiogalactoside plus cyclic AMP resulted in enhanced synthesis of the lactose permease so that galactosides relieved inhibition of glycerol uptake. Thiodigalactoside also relieved the inhibition of glycerol uptake caused by the presence of other PTS substrates such as fructose, mannitol, glucose, 2-deoxyglucose, and 5-thioglucose. Inhibition of adenylate cyclase activity by methyl-alpha-glucoside was also relieved by thiodigalactoside in E. coli T52RT provided that the lactose permease protein was induced to high levels. Cooperative binding of sugar and enzyme III(Glc) to the melibiose permease in Salmonella typhimurium was demonstrated, but no cooperativity was noted with the glycerol and maltose permeases. These results are consistent with a mechanism of PTS-mediated regulation of the lactose and melibiose permeases involving a fixed number of allosteric regulatory proteins (enzyme III(Glc)) which may be titrated by the increased number of substrate-activated permease proteins. This work suggests that the cooperativity in the binding of sugar substrate and enzyme III(Glc) to the permease, demonstrated previously in in vitro experiments, has mechanistic significance in vivo. It substantiates the conclusion that PTS-mediated regulation of non-PTS permease activities involves direct allosteric interaction between the permeases and enzyme III(Glc), the postulated regulatory protein of the PTS.

2-Ketobutyrate: a putative alarmone of Escherichia coli

2-ketobutyrate is synthesized from threonine by threonine deaminase (dehydratase) in E. coli. The effects of 2-ketobutyrate as a regulatory metabolite were studied in vivo. 2-ketobutyrate was shown to inhibit the phosphoenolpyruvate (PEP): sugar phosphotransferase system resulting in aspartate starvation, elevation of ppGpp endogenous pools, and cessation of growth in E. coli grown in glucose and related carbon sources. Accordingly, we propose that 2-ketobutyrate might serve as an alarmone whose concentration precisely governs the shift from anaerobic growth to aerobic growth in E. coli. Such shifts are common phenomena among the Enterobacteriaceae.

Regulation of glycolysis and sugar phosphotransferase activities in Streptococcus lactis: growth in the presence of 2-deoxy-D-glucose

Streptococcus lactis K1 has the capacity to grow on many sugars, including sucrose and lactose, in the presence of high levels (greater than 500 mM) of 2-deoxy-D-glucose. Initially, growth of the organism was transiently halted by the addition of comparatively low concentrations (less than 0.5 mM) of the glucose analog to the culture. Inhibition was coincident with (i) rapid accumulation of 2-deoxy-D-glucose 6-phosphate (ca. 120 mM) and preferential utilization of phosphoenolpyruvate via the mannose:phosphotransferase system, (ii) depletion of phosphorylated glycolytic intermediates, and (iii) a 60% reduction in intracellular ATP concentration. During the 5- to 10-min period of bacteriostasis the intracellular concentration of 2-deoxy-D-glucose 6-phosphate rapidly declined, and the concentrations of glycolytic intermediates were restored to near-normal levels. When growth resumed, the cell doubling time (Td) and the steady-state levels of 2-deoxy-D-glucose 6-phosphate maintained by the cells were dependent upon the medium concentration of 2-deoxy-D-glucose. Resistance of S. lactis K1 to the potentially toxic analog was a consequence of negative regulation of the mannose:phosphotransferase system by two independent mechanisms. The first, short-term response occurred immediately after the initial "overshoot" accumulation of 2-deoxy-D-glucose 6-phosphate, and this mechanism reduced the activity (fine control) of the mannose:phosphotransferase system. The second, long-term mechanism resulted in repression of synthesis (coarse control) of enzyme IImannose. The two regulatory mechanisms reduced the rate of 2-deoxy-D-glucose translocation via the mannose:phosphotransferase system and minimized the activity of the phosphoenolpyruvate-dependent futile cycle of the glucose analog (J. Thompson and B. M. Chassy, J. Bacteriol. 151:1454-1465, 1982). Phosphoenolpyruvate was thus conserved for transport of the growth sugar and for generation of ATP required for biosynthetic and work functions of the growing cell.

Comparative study of Streptococcus mutans laboratory strains and fresh isolates from carious and caries-free tooth surfaces and from subjects with hereditary fructose intolerance

This study was undertaken to investigate and compare some biochemical and physiological properties related to sugar metabolism of 4 laboratory strains and 13 freshly isolated strains of Streptococcus mutans from carious and caries-free tooth surfaces and from subjects with hereditary fructose intolerance. Growth in Trypticase (BBL Microbiology Systems)-yeast extract in the presence of various sugars was almost the same for all of the fresh isolates, which grew generally better than the laboratory strains. This was especially noticeable on sucrose where the fresh isolates (including those isolated from hereditary-fructose-intolerant patients) grew two to four times more rapidly than the laboratory strains. The rate of acid production by the fresh isolates, measured with resting cells in the presence of glucose, was quite comparable to the rate of the laboratory strains. The glucose analog, 2-deoxyglucose, inhibited the acid production from glucose by two laboratory strains (6715 and ATCC 27352), but none of the fresh isolates was affected by its presence. The antibiotic, gramicidin D, which allows free diffusion of H(+) across the cell membrane, inhibited the acid production of all of the strains. Phosphoenolpyruvate phosphotransferase activity toward alpha-methylglucoside was found in all of the laboratory and freshly isolated strains. 2-Deoxyglucose phosphotransferase activity was detected in all of the laboratory strains, but many clinical strains, especially those from hereditary-fructose-intolerant patients, contained very low or almost undetectable 2-deoxyglucose phosphotransferase activity. In one strain, the activity was restored after repeated culturing in Trypticase-yeast extract medium supplemented with glucose. Glucokinase and lactate dehydrogenase activities were detected in all of the strains tested. No marked differences were observed for these two enzymes between the fresh isolates and the laboratory strains except for three clinical strains which possessed low levels of glucokinase. The growth of all of the strains in a broth containing 4 mM glucose and 4 mM lactose was studied. Various patterns were observed: diauxie, glucose utilized before lactose but without diauxie, both sugars consumed concurrently, and lactose consumed more rapidly than glucose.

Adenylate cyclase is required for chemotaxis to phosphotransferase system sugars by Escherichia coli

We report that in Escherichia coli, chemotaxis to sugars transported by the phosphotransferase system is mediated by adenylate cyclase, the nucleotide cyclase linked to the phosphotransferase system. We conclude that adenylate cyclase is required in this chemotaxis pathway because mutations in the cyclase gene (cya) eliminate or impair the response to phosphotransferase system sugars, even though other components of the phosphotransferase system known to be required for the detection of these sugars are relatively unaffected by such mutations. Moreover, merely supplying the mutant bacteria with the products of this enzyme, cyclic AMP and cyclic GMP, does not restore the chemotactic response. Because a residual chemotactic response is observed in certain strains with residual cyclic GMP synthesis but no cyclic AMP synthesis, it appears that the guanylate cyclase activity rather than the adenylate cyclase activity of the enzyme may be required for chemotaxis to sugars transported by the phosphotransferase system. Mutations in the cyclic nucleotide phosphodiesterase gene, which increase the level of both cyclic AMP and cyclic GMP, also reduce chemotaxis to these sugars. Therefore, it appears that control of the level of a cyclic nucleotide is critical for the chemotactic response to phosphotransferase system sugars.

Regulation of hexitol catabolism in Streptococcus mutans

Regulation of hexitol catabolism was investigated in Streptococcus mutans, a cariogenic human dental plaque bacterium. Induction of hexitol catabolic enzymes and phosphoenolpyruvate:hexitol phosphotransferase and hexitol phosphate dehydrogenase activities was regulated by an inducer exclusion mechanism initiated by D-glucose and 2-deoxy-D-glucose. Kinetic analysis of the inhibitory effect of 2-deoxy-D-glucose on initial hexitol uptake illustrated that this was a noncompetitive type of inhibition. In mutant strains of S. mutans lacking phosphoenolpyruvate:glucose phosphotransferase activity, 2-deoxy-D-glucose was unable to inhibit hexitol uptake. These observations provide evidence for possible molecular mechanisms for the exclusion process.

Sequence of the malK gene in E.coli K12

We present the sequence of gene malK which encodes a component of the system for maltose transport in E.coli K12. We also determined the position of deletion (S50) which fuses malK to the following gene lamB; the malK-lamB protein hybrid contains all of the malK protein. The mRNA corresponding to the last two thirds of gene malK could form stable stem and loop structures. The malK protein, as deduced from the gene sequence, would include 370 residues and correspond to a molecular weight of 40700. The sequence as well as sequence comparisons with the ndh protein of E.coli are discussed in terms of the location and function of the malK protein.

Novel phosphoenolpyruvate-dependent futile cycle in Streptococcus lactis: 2-deoxy-D-glucose uncouples energy production from growth

The addition of 2-deoxy-D-glucose to cultures of Streptococcus lactis 133 that were growing exponentially on sucrose or lactose reduced the growth rate by ca. 95%. Inhibition did not occur with glucose or mannose as the growth sugar. The reduction in growth rate was concomitant with rapid accumulation of the analog in phosphorylated form (2-deoxy-D-glucose 6-phosphate) via the phosphoenolpyruvate-dependent mannose:phosphotransferase system. Within 5 min the intracellular 2-deoxy-D-glucose 6-phosphate concentration reached a steady-state level of greater than 100 mM. After maximum accumulation of the sugar phosphate, the rate of sucrose metabolism (glycolysis) decreased by only 30%, but the cells were depleted of fructose-1,6-diphosphate. The addition of glucose to 2-deoxy-D-glucose 6-phosphate preloaded cells caused expulsion of 2-deoxy-D-glucose and a resumption of normal growth. S. lactis 133 contained an intracellular Mg2+-dependent, fluoride-sensitive phosphatase which hydrolyzed 2-deoxy-D-glucose 6-phosphate (and glucose 6-phosphate) to free sugar and inorganic phosphate. Because of continued dephosphorylation and efflux of the non-metabolizable analog, the maintenance of the intracellular 2-deoxy-D-glucose 6-phosphate pool during growth stasis was dependent upon continued glycolysis. This steady-state condition represented a dynamic equilibrium of: (i) phosphoenolpyruvate-dependent accumulation of 2-deoxy-D-glucose 6-phosphate, (ii) intracellular dephosphorylation, and (iii) efflux of free 2-deoxy-D-glucose. This sequence of events constitutes a futile cycle which promotes the dissipation of phosphoenolpyruvate. We conclude that 2-deoxy-D-glucose functions as an uncoupler by dissociating energy production from growth in S. lactis 133.

Metabolic basis for the isoleucine, pantothenate or methionine requirement of ilvG strains of Salmonella typhimurium

Salmonella typhimurium strain DU501, which was found to be deficient in acetohydroxy acid synthase II (AHAS II) and to possess elevated levels of transaminase B and biosynthetic threonine deaminase, required isoleucine, methionine, or pantothenate for growth. This strain accumulated alpha-ketobutyrate and, to a lesser extent, alpha-aminobutyrate. We found that alpha-ketobutyrate was a competitive substrate for ketopantoate hydroxymethyltransferase, the first enzyme in pantothenate biosynthesis. This competition with the normal substrate, alpha-ketoisovalerate, limited the supply of pantothenate, which resulted in a requirement for methionine. Evidence is presented to support the conclusion that the ambivalent requirement for either pantothenate or methionine is related to a decrease in succinyl coenzyme A, which is produced from pantothenate and which is an obligatory precursor of methionine biosynthesis. The autointoxification by endogenously produced alpha-ketobutyrate could be mimicked in wild-type S. typhimurium by exogenously supplied alpha-ketobutyrate or salicylate, a known inhibitor of pantothenate biosynthesis. The accumulation of alpha-ketobutyrate was initiated by the inability of the residual AHAS activity provided by AHAS I to efficiently remove the alpha-ketobutyrate produced by biosynthetic threonine deaminase. The accumulation of alpha-ketobutyrate was amplified by the action of transaminase B, which decreased the isoleucine pool by catalyzing the formation of alpha-keto-beta-methylvalerate and aminobutyrate from isoleucine and alpha-ketobutyrate; this resulted in release of threonine deaminase from end product inhibition and unbridled production of alpha-ketobutyrate. Isoleucine satisfied the auxotrophic requirement of the AHAS II-deficient strain by curtailing the activity of threonine deaminase. Additional lines of evidence based on genetic and physiological experiments are presented to support the basis for the autointoxification of strain DU501 as well as other nonpolarigenic ilvG mutant strains.

Phosphoenolpyruvate:sugar phosphotransferase system-mediated regulation of carbohydrate metabolism in Salmonella typhimurium

The crr mutation was shown to affect the phosphoenolpyruvate:sugar phosphotransferase system-mediated transient repression of the lac operon, intracellular cAMP levels, and sensitivity to inducer exclusion. Our results indicate that the presumed crr gene product, factor IIIGlc, plays a direct role in the regulation of inducer exclusion. We propose a mechanism in which inducer exclusion depends on both the level and state of phosphorylation of factor IIIGlc and the level of an inducer exclusion-sensitive transport system. The results of studies on the sensitivity to inducer exclusion of glycerol and maltose in cultures induced for short periods of time on these substrates (resulting in varying degrees of activity of the respective transport systems) support this model of inducer exclusion. Previously, the crp*-771 mutation has been shown to result in an altered cAMP receptor protein, which has a changed affinity for cAMP, and to affect the sensitivity for inducer exclusion of glycerol. Changes in other functions of the altered cAMP receptor protein were indicated by our results; these changes were in the roles of this protein in (i) the cAMP-dependent initiation of transcription of the lac operon and (ii) the regulation of intracellular cAMP levels and the export of cAMP. We propose that the crp*-771 mutation has an indirect effect in relieving inducer exclusion in repressed or hypersensitive strains, in which the crp*-771 mutation allows the synthesis of inducer exclusion-sensitive transport systems to higher levels than the levels found in strains containing wild-type cAMP receptor protein.

Regulation of lactose permease activity by the phosphoenolpyruvate:sugar phosphotransferase system: evidence for direct binding of the glucose-specific enzyme III to the lactose permease

Interaction between the glucose-specific enzyme III (enzyme IIIglc) of the phosphoenolpyruvate:sugar phosphotransferase system and the lactose permease was studied with membrane fragments from an Escherichia coli strain that overproduces the lactose permease. Substrates of the permease markedly and specifically stimulated binding of enzyme IIIglc to the membranes. The sugar-stimulated binding of enzyme IIIglc was concluded to the specific to the lactose permease because it (i) was dependent on the amount of the permease, (ii) was promoted only by sugar substrates of the permease, and (iii) was completely eliminated by treatment of the membranes with N-ethylmaleimide in the absence (but not the presence) of thio-beta-D-digalactoside. The pH dependence of binding was similar to that reported for the binding of thio-beta-D-digalactoside to the permease. Phosphoenolpyruvate prevented the binding of enzyme IIIglc to the lactose permease in the presence (but not the absence) of the other phosphate transfer components of the phosphotransferase system. These results support the hypothesis that enzyme IIIglc, in its dephosphorylated form, modulates the activity of the lactose permease by a direct protein-protein interaction.

Regulation of L-arabinose transport in Salmonella typhimurium LT2

The inducible L-arabinose transport system was characterized in Salmonella typhimurium LT2. Only one L-arabinose transport system with a Km of 2 X 10(-4) M was identified. The results suggested that araE may be the only gene which codes for L-arabinose transport activity under the conditions tested. An araE-lac fusion strain was used to study the induction of the araE gene. No araE expression was detected when the L-arabinose concentration was lower than 1 mM. The expression of araE reached a maximum in the presence of 50 mM L-arabinose, and was significantly reduced in the presence of 50 mM L-arabinose, and was significantly reduced in the presence of D-glucose. Expression of the araBAD and araE genes was coordinately regulated. The concentration of L-arabinose that allowed maximum araBAD gene expression was 50-fold lower in an araE+ strain compared to an araE strain.

Characterization and genetic mapping of fructose phosphotransferase mutations in Pseudomonas aeruginosa

Pseudomonas aeruginosa transports and phosphorylates fructose via a phosphoenolpyruvate-dependent fructose phosphotransferase system (PTS). Mutant strains deficient in both PTS activity and glucose-6-phosphate dehydrogenase activity were isolated and were used to select mannitol-utilizing revertant strains singly deficient in PTS activity. These mutants were unable to utilize fructose as a carbon source and failed to accumulate exogenously provided [14C]fructose, and crude cell extracts lacked phosphoenolpyruvate-dependent fructose PTS activity. Thus, the PTS was essential for the uptake and utilization of exogenously provided fructose by P. aeruginosa. Mutations at a locus designated pts, which resulted in a loss of PTS activity, exhibited 57% linkage to argF at 55 min on the chromosome in plasmid R68.45-mediated conjugational crosses. The pts mutations in four independently isolated mutant strains exhibited from 11 to 20% linkage to argF, and one of these mutations exhibited 3% linkage to lys-9015 in phage F116L-mediated transductional crosses.

Characterization of factor IIIGLc in catabolite repression-resistant (crr) mutants of Salmonella typhimurium

crr mutants of Salmonella typhimurium are thought to be defective in the regulation of adenylate cyclase and a number of transport systems by the phosphoenolpyruvate-dependent sugar phosphotransferase system, crr mutants are also defective in the enzymatic activity of factor IIIGlc (IIIGlc), a protein component of the phosphotransferase system involved in glucose transport. Therefore, it has been proposed that IIIGlc is the primary effector of phosphotransferase system-mediated regulation of cell metabolism. We characterized crr mutants with respect to the presence and function of IIIGlc by using an immunochemical approach. All of the crr mutants tested had low (0 to 30%) levels of IIIGlc compared with wild-type cells, as determined by rocket immunoelectrophoresis. The IIIGlc isolated from one crr mutant was investigated in more detail and showed abnormal aggregation behavior, which indicated a structural change in the protein. These results supported the hypothesis that a crr mutation directly affects IIIGlc, probably by altering the structural gene of IIIGlc. Several crr strains which appeared to be devoid of IIIGlc in immunoprecipitation assays were still capable of in vitro phosphorylation and transport of methyl alpha-glucoside. This phosphorylation activity was sensitive to specific anti-IIIGlc serum. Moreover, the membranes of crr mutants, as well as those of wild-type cells, contained a protein that reacted strongly with our anti-IIIGlc serum. We propose that S. typhimurium contains a membrane-bound form of IIIGlc which may be involved in phosphotransferase system activity.

Fractionation and characterization of the phosphoenolpyruvate: fructose 1-phosphotransferase system from Pseudomonas aeruginosa

The initial reactions involved in the catabolism of fructose in Pseudomonas aeruginosa include the participation of a phosphoenolpyruvate:fructose 1-phosphotransferase system (F-PTS). Fractionation of crude extracts of fructose-grown cells revealed that both membrane-associated and soluble components were essential for F-PTS activity. Further resolution of the soluble fraction by both size exclusion and ion-exchange chromatography revealed the presence of only one component, functionally analogous to enzyme I. Enzyme I exhibited a relative molecular weight of 72,000, catalyzed the pyruvate-stimulated hydrolysis of phosphoenolpyruvate to pyruvate, and mediated the phosphorylation of fructose when combined with a source of enzyme II (washed membranes). No evidence for the requirement of a phosphate carrier protein, such as HPr, could be demonstrated. Thus, the F-PTS requires a minimum of two components, a soluble enzyme I and a membrane-associated enzyme II complex, and both were shown to be inducible. Reconstituted F-PTS activity was specific for phosphoenolpyruvate as a phosphate donor (Km, approximately -0.6 mM) and fructose as the sugar substrate (Km, approximately 18 microM). Components of the Pseudomonas F-PTS did not restore activity to extracts of deletion mutants of Salmonella typhimurium deficient in individual proteins of the PTS or to fractionated membrane and soluble components of the F-PTS of Escherichia coli. Similarly, membrane and soluble components of E. coli and S. typhimurium would not cross-complement the F-PTS components from P. aeruginosa.

Plasmid-directed synthesis of enzymes required for D-mannitol transport and utilization in Escherichia coli

A transformant Escherichia coli colony bank [Clarke, L. & Carbon, J. (1976) Cell 9, 91-99] has been screened for hybrid ColE1 plasmids carrying the genes for D-mannitol utilization. Two of the plasmids, pLC11-7 and pLC15-48, were shown to contain the mannitol operon, which includes the structural genes for the mannitol-specific enzyme II of the phosphotransferase system and mannitol-1-phosphate dehydrogenase. One E. coli strain harboring plasmid pLC15-48 overproduced mannitol-1-phosphate dehydrogenase activity 4- to 5-fold. However, there was no corresponding increase in mannitol enzyme II activity. Plasmid pLC15-48 was shown to direct the synthesis of two polypeptides in E. coli minicells in the presence of cyclic AMP and mannitol. The larger (Mr = 60,000) was membrane bound and was specifically precipitated by antibody directed against purified mannitol-specific enzyme II. The smaller (Mr = 40,000) was soluble and had an electrophoretic mobility indistinguishable from that of the major component in a partially purified mannitol-1-phosphate dehydrogenase preparation. These data are consistent with previous genetic studies of the mannitol locus and confirm an independent conclusion [Jacobson, G. R., Lee, C. A. & Saier, M. H., Jr. (1979) J. Biol. Chem. 254, 249-252] that mannitol enzyme II consists of a single type of polypeptide chain that has a Mr of 60,000. The plasmid pLC15-48 DNA was characterized by mapping of restriction endonuclease cleavage sites.

Isolation of IIIGlc of the phosphoenolpyruvate-dependent glucose phosphotransferase system of Salmonella typhimurium

We report a procedure for the isolation of IIIglc of Salmonella typhimurium, a protein component of the phosphoenolpyruvate-dependent sugar phosphotransferase system. IIIGlc is a soluble protein with a molecular weight of 21,000, as determined by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified protein is involved in the phosphoenolpyruvate-dependent phosphorylation of methyl alpha-glucoside in vitro. Its affinity for octyl-Sepharose may be an indication of the partial hydrophobic nature of IIIGlc. A specific antiserum against purified IIIGlc was prepared. Growth on different carbon sources did not affect the synthesis of IIIGlc, as determined by quantitative immunoelectrophoresis. Mutations which lower the adenosine 3',5'-phosphate level, such as cya and pts, do not alter the IIIGlc level. The closely related enteric bacteria Escherichia coli and Klebsiella aerogenes contain a protein factor which is closely related to IIIGlc of S. typhimurium, whereas Staphylococcus aureus does not.

The phosphoenolpyruvate-dependent carbohydrate: phosphotransferase system enzymes II as chemoreceptors in chemotaxis of Escherichia coli K 12

In Escherichia coli K12, eight substrate-specific, membrane-bound enzymes II of the PEP-dependent carbohydrate: phosphotransferase system (PTS), specific for hexoses, hexosamines and hexitols, have been characterised in a series of isogenic and constitutive strains. In such mutants, lacking all but one enzyme II, the transport and vectorial phosphorylation activities as well as the chemotactical response in capillary tube assays have been compared. According to the data obtained, all enzymes II not only are directly involved in the transport and vectorial phosphorylation of their substrates, but they have also a primary role as the chemoreceptors for these substrates: (1) Metabolism of the attractant beyond the phosphorylation step is not a pre-requisite to eliciting positive chemotaxis. (2) Mutants, having only one enzyme II react in the capillary tube assay only to substrates of this enzyme II, but not to substrates of the missing enzymes II. This holds for enzymes II consisting of one membrane-bound protein as well as for systems containing a soluble factor III (FIII). (3) The substrate specificities or affinities, whether tested by transport and chemotaxis assays in vivo or by phosphorylation tests in vitro, are in correspondence. (4) The activities of enzymes II, regulated in a complex way at the level of enzyme synthesis and activity and tested as above, are also in agreement, (5) Mutants lacking the soluble proteins enzyme I or HPr of the PTS no longer respond chemotactically to any substrate taken up and phosphorylated by enzymes II. It is concluded that in PTS enzymes II some functions required for transport and chemotaxis are identical. It is suggested furthermore, that the alternation of intrinsic membrane-bound proteins between a phosphorylated and a dephosphorylated state, rather than binding of the substrate to the enzyme II, is the decisive stimulus in the chemotaxis toward carbohydrates taken up by these transport systems.

Relationship of Cell Envelope Stability to Substrate Capture in a Marine Psychrophilic Bacterium

Cells of a psychrophilic marine bacterium were found to take up a variety of amino acids from seawater. Some of the amino acids that were taken up were released when the cells were exposed to a hypotonic salt solution. The proportion that was released varied according to the amino acid. A pool of the amino acid arginine that was formed during very short periods of exposure of cells to the exogenously supplied amino acid was particularly sensitive to reductions in salinity. In general, exposure to hypotonic salt solutions also resulted in reduced amino acid uptake by the cells. Complete removal of seawater salts (SE treatment) produced obvious structural alterations in the cell envelope, resulting in an even greater reduction in amino acid uptake. Under these conditions, amino acid-binding components were released by the cells. Differential centrifugation and fluorescent antibody studies indicated that arginine-binding components are located on or near the surface of intact cells. The data suggest that substrate receptors were sensitive to reductions in seawater salt concentrations and that lesions at this level affected the organism's substrate uptake and retention capabilities.

Regulation of methyl-beta-d-thiogalactopyranoside-6-phosphate accumulation in Streptococcus lactis by exclusion and expulsion mechanisms

Starved cells of Streptococcus lactis ML3 (grown previously on galactose, lactose, or maltose) accumulated methyl-beta-D-thiogalactopyranoside (TMG) by the lactose:phosphotransferase system. More than 98% of accumulated sugar was present as a phosphorylated derivative, TMG-6-phosphate (TMG-6P). When a phosphotransferase system sugar (glucose, mannose, 2-deoxyglucose, or lactose) was added to the medium simultaneously with TMG, the beta-galactoside was excluded from the cells. Galactose enhanced the accumulation of TMG-6P. Glucose, mannose, lactose, or maltose plus arginine, was added to a suspension of TMG-6P-loaded cells of S. lactis ML3, elicited rapid expulsion of intracellular solute. The material recovered in the medium was exclusively free TMG. Expulsion of galactoside required both entry and metabolism of an appropriate sugar, and intracellular dephosphorylation of TMG-6P preceded efflux of TMG. The rate of dephosphorylation of TMG-6P by permeabilized cells was increased two-to threefold by adenosine 5'-triphosphate but was strongly inhibited by fluoride. S. lactis ML3 (DGr) was derived from S. lactis ML3 by positive selection for resistance to 2-deoxy-D-glucose and was defective in the enzyme IIMan component of the glucose:phosphotransferase system. Neither glucose nor mannose excluded TMG from cells of S. lactic ML3 (DGr), and these two sugars failed to elicit TMG expulsion from preloaded cells of the mutant strain. Accumulation of TMG-6P by S. lactis ML3 can be regulation by two independent mechanisms whose activities promote exclusion or expulsion of galactoside from the cell.

Genetic characterization of the araE gene in Salmonella typhimurium lt2

Six L-arabinose transport-deficient mutants of Salmonella typhimurium LT2 were isolated on the basis of their inability to ferment low concentrations of L-arabinose. The mutations were localized between serA and lys on the S. typhimurium genetic map and assigned to the araE locus. An araE-lac fusion strain was constructed and used to determine that the direction of araE transcription was counterclockwise on the S. typhimurium genetic map. beta-Galactosidase activity was induced by L-arabinose in the araE-lac fusion strain, suggesting that araE expression is controlled at the level of transcription.

Relationship between the Na+/H+ antiporter and Na+/substrate symport in Bacillus alcalophilus

The Na+/H+ antiporter of the obligate alkalophile Bacillus alcalophilus facilitates growth at alkaline pH and precludes growth below pH 8.5. Thus, nonalkalophilic mutant strains do not exhibit Na+/H+ antiport activity and, interestingly, such strains concomitantly lose the ability to catalyze Na+-dependent accumulation of alpha-aminoisobutyrate [Krulwich, T. A., Mandel, D. G. Bornstein, R. F. & Guffanti, A. A. (1979) Biochem. Biophys. Res. Commun. 91, 58-62]. Several other Na+-dependent transport systems are now documented in vesicles from the wild-type strain, and it is demonstrated that these systems are defective in vesicles from the nonalkalophilic mutant KM23. Surprisingly, the defect seems to result not from the loss of Na+/H+ antiport activity per se but from a pleiotropic defect in the Na+/substrate symporters themselves. Monensin, an ionophore that catalyzes Na+/H+ exchange, does not restore respiration-driven Na+/substrate symport in KM23 vesicles. Moreover, with KM23 vesicles, efflux of alpha-aminoisobutyrate, L-malate, and L-aspartate down their respective concentration gradients is not stimulated by Na+, in contrast to the observations with wild-type vesicles. Because monensin should ameliorate a simple defect in Na+/H+ antiport activity and the antiporter should not be required for Na+/substrate symport down a concentration gradient, the results suggest that there may be a direct relationship between the antiporter and various Na+/substrate symporters. One possibility is that the systems share a Na+-translocating subunit.

Vectorial and nonvectorial transphosphorylation catalyzed by enzymes II of the bacterial phosphotransferase system

Vectorial transphosphorylation of hexitols, catalyzed by enzymes II of the bacterial phosphotransferase system, was studied in intact cells and membrane vesicles of Escherichia coli. In strains depleted of phosphoenolpyruvate and unable to metabolize the internal hexitol phosphate, internal mannitol-1-phosphate stimulated uptake of extracellular [14C]mannitol, whereas external mannitol stimulated release of [14C]mannitol from the intracellular [14C]mannitol-1-phosphate pool. The stoichiometry of mannitol uptake to mannitol release was 1:1. Glucitol did not promote release of [14C]mannitol from the mannitol phosphate pool but stimulated release of [14C]glucitol from internal glucitol phosphate pools when the glucitol enzyme II was induced to high levels. In E coli cells and membrane vesicles, both vectorial and nonvectorial transphosphorylation reactions of hexitols and hexoses were demonstrated. The nonvectorial reactions, but not the vectorial reactions, catalyzed by the mannitol and glucose enzymes II, were inhibited by p-chloromercuriphenyl sulfonate, a membrane-impermeable sulfhydryl reagent which inactivates enzymes II. Similarly, glucose-6-sulfate, an inhibitor of the glucose enzyme II-catalyzed transphosphorylation reaction, specifically inhibited the nonvectorial reaction. This compound was shown to be a noncompetitive inhibitor of methyl alpha-glucoside phosphorylation employing phospho-HPr as the phosphate donor. It apparently exerts its inhibitory effect by exclusive binding to the sugar phosphate binding site on the enzyme II complex. The results are consistent with the conclusion that enzymes II can exist in two distinct dispositions in the membrane, one of which catalyzes vectorial transphosphorylation, and the other catalyzes nonvectorial transphosphorylation.