Role of lipids in the biosynthesis of the bacterial cell envelope

High-Level Production of Lacto-N-neotetraose in Escherichia coli by Stepwise Optimization of the Biosynthetic Pathway

Lacto-N-neotetraose (LNnT), an abundant human milk oligosaccharide (HMO), has been approved as a novel functional additive for infant formulas. Therefore, LNnT biosynthesis has attracted extensive attention. Here, a high LNnT-producing, low lacto-N-triose II (LNT II)-residue Escherichia coli strain was constructed. First, an initial LNnT-producing chassis strain was constructed by blocking lactose, UDP-N-acetylglucosamine, and UDP-galactose competitive consumption pathways and introducing β-1,3-N-acetylglucosaminyltransferase LgtA and β-1,4-galactosyltransferase LgtB. Subsequently, the supply of LNnT precursors was increased by enhancing UDP-N-acetylglucosamine and UDP-galactose synthesis, inactivating LNT II extracellular transporter SetA, and improving UTP synthesis. Then, modular engineering strategy was used to optimize LNnT biosynthetic pathway fluxes. Moreover, pathway fluxes were fine-tuned by modulating translation initiation strength of essential genes lgtB, prs, and lacY. Finally, LNnT production reached 6.70 g/L in a shake flask and 19.40 g/L in a 3 L bioreactor with 0.47 g/(L h) productivity, with 1.79 g/L LNT II residue, highest productivity level, and lowest LNT II residue thus far.

Conserved structural regions involved in the catalytic mechanism of Escherichia coli K-12 WaaO (RfaI)

Escherichia coli K-12 WaaO (formerly known as RfaI) is a nonprocessive alpha-1,3 glucosyltransferase, involved in the synthesis of the R core of lipopolysaccharide. By comparing the amino acid sequence of WaaO with those of 11 homologous alpha-glycosyltransferases, four strictly conserved regions, I, II, III, and IV, were identified. Since functionally related transferases are predicted to have a similar architecture in the catalytic sites, it is assumed that these four regions are directly involved in the formation of alpha-glycosidic linkage from alpha-linked nucleotide diphospho-sugar donor. Hydrophobic cluster analysis revealed a conserved domain at the N termini of these alpha-glycosyltransferases. This domain was similar to that previously reported for beta-glycosyltransferases. Thus, this domain is likely to be involved in the formation of beta-glycosidic linkage between the donor sugar and the enzyme at the first step of the reaction. Site-directed mutagenesis analysis of E. coli K-12 WaaO revealed four critical amino acid residues.

Phospholipid domains determine the spatial organization of the Escherichia coli cell cycle: the membrane tectonics model

Escherichia coli normally divides at its equator between segregated nucleoids. Such division is inhibited during perturbations of chromosome replication (even in the absence of inducible division inhibitors); eventually, division resumes at sites which are not at this equator. Escherichia coli will also divide at its poles to generate minicells following overproduction of the FtsZ or MinE proteins. The mechanisms underlying the division inhibition and the positioning of the division sites are unknown. In the membrane tectonics model, I propose that the formation of phospholipid domains within the cytoplasmic membrane positions division sites. The particular phospholipid composition of a domain attracts particular proteins and determines their activity; conversely, particular proteins change the composition of domains. Principally via such proteins, the interaction of the chromosome with the membrane creates a chromosomal domain. The development of chromosomal domains during replication and nucleoid formation contributes to the formation and positioning of a septal domain between them. During septation (cell division), this septal domain matures into a polar domain. Each domain attracts and activates different enzymes. The septal domain attracts and activates enzymes necessary for septation. Preventing the formation of the septal domain by preventing chromosome replication prevents normal division. Altering the composition of the polar domain may allow septation enzymes to function there and generate minicells. A corollary of the model explains how the formation of an origin domain by the attachment of hemi-methylated origin DNA to the membrane may underlie the creation and migration of structures within the envelope, the periseptal annuli.

Specific binding of lipopolysaccharides to mouse macrophages--I. Characteristics of the interaction and inefficiency of the polysaccharide region

Tritium-labeled lipopolysaccharide interacted specifically and reversibly with mouse peritoneal macrophages. The binding was higher at 22 degrees C than at 4 degrees C, but was no longer observable at 37 degrees C. The specificity of the interaction (inhibition with unlabeled LPS) was strictly dependent on the presence of serum, and required divalent cations. The binding was saturable. The specific binding sites of peritoneal macrophages were saturated with 6-9 x 10(6) LPS molecules/cell, and those of macrophage-like cell lines with 2-3 x 10(6) molecules/cell. The binding of LPS was not inhibited by ligands of scavenger receptors (maleylated BSA) or complement receptors (zymosan), but was strongly inhibited with dexamethasone, a glucocorticoid which is known to modulate the expression of other surface markers of macrophages. The polysaccharide region of the LPS, as well as 3-deoxy-2-octulosonic acid (KDO) coupled to bovine serum albumin, did not bind to macrophages, whereas a specific binding was observed with a lipid A-BSA conjugate.

Outer membrane polysaccharide deficiency in two nongliding mutants of Cytophaga johnsonae

Phenol-extractable polysaccharides firmly associated with the outer membrane of the gliding bacterium Cytophaga johnsonae could be resolved by gel filtration in sodium dodecyl sulfate (SDS) or by SDS-polyacrylamide gel electrophoresis into a high-molecular-weight (H) fraction (excluded by Sephadex G-200) and a low-molecular-weight (L) fraction. Fraction L was rich in components typical of lipid A and the core region of lipopolysaccharide (P, 3-hydroxy fatty acids, and 2-keto-3-deoxyoctonate) and evidently was a lipopolysaccharide with a limited number of distal, repeating polysaccharide units, as judged by SDS-polyacrylamide gel electrophoresis. In relation to total carbohydrate, the H fraction was rich in amino sugar but poor in (possibly devoid of) the lipid A and core components. Two nongliding mutants were highly deficient in the H fraction; one of these was deficient in sulfonolipid but could be cured by provision of a specific sulfonolipid precursor, a process that also resulted in the return of both the H fraction and gliding, as well as the ability to move polystyrene latex spheres over the cell surface. Hence, the polysaccharide may be the component that is directly involved in motility, and the presence of sulfonolipids in the outer membrane is necessary for the synthesis or accumulation of the polysaccharide. This conclusion was reinforced by the fact that the second nongliding, polysaccharide-deficient mutant had a normal sulfonolipid content.

Membrane glycolipid and phospholipid composition of lipopolysaccharide-responsive and -nonresponsive murine B lymphocytes

Neutral glycolipids, gangliosides, and phospholipids present on membranes of unstimulated or lipopolysaccharide (LPS)-stimulated B cells were analyzed in LPS-responsive C3H/HePAS and LPS-nonresponsive C3H/HeJ mice. In the set of neutral glycolipids, asialo GM1 reacted preferentially with galactose oxidase but was not detectable with monospecific antibodies during immunocytofluorescence analysis. Another, more polar, neutral glycolipid appeared exclusively after stimulation of responsive B cells. Among the membrane gangliosides 1 to 5 that were able to react with galactose oxidase on B cells, ganglioside 3 was not detected in the mutant strain, and its absence was counterbalanced by the presence of a larger amount of ganglioside 1. The biosynthesis of total membrane phospholipids and the balance between phosphatidylethanolamine and phosphatidylcholine were significantly different in the two mouse strains examined and were quantitatively and qualitatively modified during the mitogenic response to LPS.

Modulation of murine lymphocyte mitogen responses by glycerol-teichoic acid

Glycerol-teichoic acid (GTA) showed a modulatory effect on the in vitro response of murine splenocytes to the mitogens concanavalin A (Con A) and lipopolysaccharide (LPS) as measured by incorporation of 3H-thymidine. GTA inhibited the response to Con A when added prior to addition of the mitogen, while addition 24 hr after had no significant effect on the response. The degree of suppression was dose dependent in a range from 0.1-5 microgram GTA/culture. The spleen cell response to LPS was enhanced by GTA when added prior to the mitogen. Peak enhancement occurred at 1-2 microgram GTA/culture, depending on the time of addition. GTA added 24 hr after LPS produced no significant effect on mitogenesis. Addition of GTA alone to spleen cell cultures produced a slight suppression of DNA synthesis and was toxic at 10 microgram/culture if incubated at least 66 hr. GTA is bound to murine spleen cells as indicated by decreased passive hemagglutination inhibition activity of culture supernates.

The binding of LPS to the lymphocyte surface

Bacterial lipopolysaccharide (LPS) from Escherichia coli labelled with tritium has been used to follow the binding of LPS to lymphocytes. Binding to cells rose to a maximum 2-7 min after addition of [3H]-LPS, followed by loss of [3H]-LPS from cells, reducing to about 10% of the peak level at 20-30 min. Peripheral blood lymphocytes, mesenteric lymph node and thymus cells of the pig and CBA, C3H/He and C3H/HeJ mouse spleen cells all bound [3H]-LPS transiently at similar levels. It is concluded that this type of LPS binding cannot be solely responsible for the preferential stimulation of B cells by LPS.

Bacterial lipopolysaccharide (LPS) enhances concanavalin A reactivity of thymocytes from the low-LPS-responder mouse strain C3H/Hej

The capacity of LPS to enhance Con A reactivity of thymocytes was studied comparatively in the low-LPS-responder C3H/Hej mice and the high-LPS-responder CBA mice. The extent of synergism LPS + Con A was found similar in both strains.

Relationship between phospholipid compositions and transport activities of amino acids in Escherichia coli membrane vesicles

Cells of Escherichia coli were incubated in broth medium in the presence of 5 mM of hydroxylamine which completely inhibited growth but did not affect viabilities. Hydroxylamine is known to inhibit phosphatidylserine decarboxylase. A large amount of phosphatidylserine (up to 20% of total phospholipids), which did not occur in normal cells, accumulated accompanied with a decrease in phosphatidylethanolamine. Higher uptake activities of serine and glutamate were observed with the hydroxylamine-treated cells than control cells. When membrane vesicles from hydroxylamine-treated cells were prepared, they also displayed higher uptake activities of serine, proline, glutamate, and threonine than those of normal membranes. When hydroxylamine-treated cells were incubated with chloramphenicol, at concentrations which almost completely inhibited protein synthesis, the composition of phosphatidylserine decreased with a concomitant increase in that of phosphatidylethanolamine. The phospholipid composition of these cells incubated for 5 h with chloramphenicol became almost normal. Membranes vesicles prepared from such cells displayed reduced uptake activities, which were close to those of normal vesicles. These results were interpreted as indicating the altered transport activities due to the altered phospholipid composition.

Ethylenediaminetetraacetic acid-sensitive antiphagocytic activity of Neisseria gonorrhoeae

Colonial types of Neisseria gonorrhoeae were examined for the presence of pilus-independent antiphagocytic activity. Type 3 and depiliated type 1 gonococci had a shearing- and protease-resistant antiphagocytic activity that was eliminated by treatment with ethylenediaminetetraacetic acid (EDTA) and that was not present on type 4 bacteria. Incubation of EDTA-treated bacteria 37 degrees C for 90 min resulted in fas prevented by antibiotics that block the final assembly of cell wall macromolecules that depend on the C55-isoprenoid carrier for export. These include both lipopolysaccharide and peptidoglycan. Restoration was, however, unaffected by drugs that interfere with the synthesis of peptidoglycan, but not that of lipopolysaccharide, and by inhibitors of protein synthesis. These data suggested that gonococci have an antiphagocytic mechanism in addition to the previously described determinant (presumably pili) that was removed by blending or by treatment with proteases. Of the two antiphagocytic activities, type 1 had both, type 3 had only the EDTA-sensitive component, and type 4 had neither.

Binding of bacterial endotoxin to murine spleen lymphocytes

The early events in lipopolysaccharide (LPS)-induced B-cell activation were investigated by studying the binding of 14C-labeled LPS to murine lymphocytes in vitro. In these studies we utilized intrinsically labeled 14C-labeled LPS from Salmonella minnesota or the 14C-labeled glycolipid derived from the Re mutant of S. minnesota (R595). Bone marrow-derived (B) lymphocytes bound more LPS than did thymus-derived (T) lymphocytes. Binding of LPS to murine spleen lymphocytes from strain C3H/HeN was compared with the binding to spleen lymphocytes from strain C3H/HeJ, a strain resistant to certain biological activities of LPS including mitogenesis. Spleen cells from both strains bound LPS equally well, suggesting that unresponsiveness of C3H/HeJ mice to LPS is due to factors other than a defect in binding of LPS. LPS binding to cells appeared to be due to a nonspecific interaction between the lipid moiety of LPS and the lipid components of the cell membrane. Thus, the highly lipophilic, polysaccharide-deficient glycolipid from R595 bound at least 20 times better than did LPS. Furthermore, partial removal of cell surface proteins with trypsin or sialic acids with neuraminidase enhanced glycolipid binding, suggesting that binding is not through a protein- or sialic acid-containing receptor. The binding of glycolipid to lymphocytes was only partially specific since unlabeled glycolipid R595, lipid A, and LPS did not completely inhibit the uptake of 14C-labeled glycolipid R595. In addition, binding could be inhibited by a nonmitogenic phospholipid (phosphatidyl ethanolamine), which also is consistent with a nonspecific lipid-lipid interaction. Experiments were performed to determine the relationship of LPS binding to lymphocyte activation in the lymphocytes. The process of activation of lymphocytes by LPS was a slow one, since LPS was required to be present in culture for at least 24 h in order to obtain significant lymphocyte activation, suggesting that the amounts of LPS bound earlier are either quantitatively or qualitatively insufficient to irreversibly activate the cell.

Local immunie response in experimental pyelonephritis in the rabbit. III. Lymphocyte responsivieness to O and K antigens of Escherichia coli

The response of circulating and infected kidney lymphocytes to the O (lipopolysaccharide) and K (polysaccharide) antigens of an Escherichia coli O6 K 13 H1 strain was determined. Both circulating and kidney lymphocytes showed significant incorporation of [3H-methyl]thymidine into DNA when incubated with the O antigen, whereas neither responded to the K antigen. The lipid moiety of the lipopolysaccharide was required for lymphocyte responsiveness. Upon sequential incubation of O antigen and fluoresceinated homologous antiserum, 24-30 per cent of kidney lymphocytes were shown to have surface receptors for O antigen, whereas none had surface receptors for K antigen. Although the K antigen is an important determinant of invasiveness of the upper urinary tract, it fails to elicit a cellular immune response or attach to lymphocytes from the infected kidney in experimental pyelonephritis.

Surface balance study of the interaction between microorganisms and lipid monolayer at the air/water interface

Using the surface balance technique, we have compared the interaction between Acholeplasma laidlawii and some marine bacteria towards different types of monolayered lipid films. Cells from A. laidlawii and Serratia marinorubra penetrate the film, whereas cells from Psuedomonas fluorescens form a layer underneath the film. The forces that bind microorganisms to the air/water interface are not strong enough to scatter a condensed monolayer but increase the strength of loosely packed monolayers.

Comparison of lipopolysaccharides from Agmenellum quadruplicatum to Escherichia coli and Salmonella typhimurium by using thin-layer chromatography

Lipopolysaccharide (LPS) was isolated from the unicellular blue-green bacterium Agmenellum quadruplicatum using the procedure of Westphal and Jann (1965). It was composed of a lipid A and polysaccharide region suggesting a similarity to other gram-negative LPSs. Chemical analyses demonstrated the presence of glucose, rhamnose, mannose, and xylose in the polysaccharide region, as well as 2-keto-3-deoxyoctonate, glucosamine, and phosphorous in the lipid A. Studies on the lipid composition revealed the presence of palmitic, behenic, and three beta-hydroxy fatty acids. A new procedure for thin-layer chromatography of bacterial LPSs was used to compare LPS from A. quadruplicatum to other gram-negative organisms. The method is capable of distinguishing between LPSs of different bacteria as well as between the wild-type organism and mutated forms unable to synthesize complete LPS. A comparison of LPS from A. quadruplicatum to Escherichia coli and Salmonella typhimurium demonstrated that, although the blue-green LPS was rather similar to that of the Enterobacteriaceae, distinct differences also existed. However, when several cell division mutants of A. quadruplicatum were compared chromatographically to the parent strain BG-1, no differences were observed. This suggests that cell division mutations in A. quadruplicatum are not associated with changes in the LPS.

A mannosyl-carrier lipid of bovine adrenal meddulla and rat parotid

1. The transfer of mannose from GDP-(U-14-C)mannose into endogenous acceptors of bovine adrenal medullla and rat parotid was studied. The rapidly labelled product, a glycolipid, was partially purified and characterized. 2. It was stable to mild alkaline hydrolysis but yielded (14-C)mannose on mild acid hydrolysis. It co-chromatographed with mannosyl phosphoryl dolichol in four t.l.c. systems and on DEAE-cellulose acetate. Addition of dolichol phosphate or a dolichol phosphate-enriched fraction prepared from pig liver stimulated mannolipid synthesis. 3. The formation of mammolipid appeared reversible, since addition of GDP to a system synthesizing the mannolipid caused a rapid loss of label from the mannolipid. UDP-N-acetylglucosamine did not inhibit mannolipid synthesis except at high concentrations (2 mM), even though in the absence of GDP-mannose, N-acetylglucosamine was incorporated into a lipid having the properties of a glycosylated polyprenyl phosphate. 4. Mannose from GDP-mannose was also incorporated into two other acceptors, (2y being insoluble in chloroform-methanol (2:1, v/v) but soluble in choloroform-methanol-water (10:10:3, by vol.) and (ii) protein. These are formed much more slowly than the mannolipid. 5. Exogenous mannolipid served as a mannose donor for acceptors (i) and (ii), and it is suggested that transfer of mannose from GDP-mannose to mannosylated protein occurs via two intermediates, the mannolipid and acceptor (i).

Association of Salmonella typhimurium with, and its invasion of, the ileal mucosa in mice

A wild-type strain of Salmonella typhimurium and three mutant rough colonial variants of the wild type were compared for their ability to become associated with and invade the ileal mucosa of germfree and specific-pathogen-free mice. The rough-mutant strains differed from the wild type in having incomplete lipopolysaccharides lacking one or more sugars in the polysaccharide moiety. The wild-type and mutant strains also differed one from the other in the types of appendages (flagella, pili) on their surfaces. Depending upon the dosage of bacteria given, all mutant strains as well as the wild type could associate with and invade the intestinal mucosa of infected gnotobiotic mice. If the infecting dosage was high enough, at least two of the mutant strains and the wild type invade the intestinal mucosa of the specific-pathogen-free animals. O antigen, flagella, or pili do not appear to be essential for the association of S. typhimurium with the mucosal surface of the mouse ileum. O antigen on the bacterial cell surface may be important, but not essential, for invasion of the ileal mucosa.

Mitogenic effect by lipopolysaccharide and pokeweed lectin on density-inhibited chick embryo fibroblasts

The B lymphocyte mitogens, bacterial lipopolysaccharide (LPS), pokeweed lectin, and tuberculin, induced proliferation in density-inhibited monolayer cultures of chick embryo fibroblasts. The stimulation was seen both as an early increase in sugar uptake and cell volume and later as an increase in thymidine incorporation and cell number. The concentration of LPS maximally stimulating fibroblasts was remarkably low, about 0.1-1 ng/ml. LPS preparation with very different sugar chains gave quite similar results indicating that the architecture of the hydrophilic carbohydrate part is not critical for the mitogenic effect.

Relationship of the structure of bacterial lipopolysaccharides to its function in mitogenesis and adjuvanticity

The ability of bacterial lipopolysaccharides to induce lymphocyte mitogenesis and to act as an adjuvant of antibody formation was attributable to the lipid-A region of the molecule. Measured by induction of DNA synthesis, lipid A was mitogenic for bone marrow-derived lymphocytes obtained from spleens of congenitally athymic mice but not for thymocytes obtained from thymuses of normal mice. Adjuvanticity was demonstrated by the ability of lipid A to convert a tolerogenic regimen of antigen into one eliciting an immune response and by its ability to markedly enhance the antibody response to a weak antigen.

Colicin B: mode of action and inhibition by enterochelin

Adsorption of colicin B to a sensitive strain of Escherichia coli results in rapid cessation of deoxyribonucleic acid, ribonucleic acid, and protein synthesis. Some classes of mutants insensitive to colicin B hyperexcrete a colicin inhibitor into their growth medium. This inhibitor functions by preventing adsorption of colicin B and does not rescue cells to which colicin has already adsorbed. The inhibitor is insensitive to nucleases, proteolytic enzymes, and lysozyme and is not extracted into organic solvents. The inhibitory material has a low molecular weight, which rules out identification as lipopolysaccharide, although purified lipopolysaccharide has some inhibitory activity. Evidence is presented that the inhibitor is enterochelin, an iron chelator which is the cyclic trimer of 2,3-dihydroxybenzoylserine. Enterochelin does not inhibit colicin M, a colicin that is produced by many strains colicinogenic for colicin B.

Regulation of beta-Glucan Synthetase Activity by Auxin in Pea Stem Tissue: II. Metabolic Requirements

The 2- to 4-fold rise in particle-bound beta-glucan synthetase (uridine diphosphate-glucose: beta-1, 4-glucan glucosyltransferase) activity that can be induced by indoleacetic acid in pea stem tissue is not prevented by concentrations of actinomycin D or cycloheximide that inhibit growth and macromolecule synthesis. The rise is concluded to be a hormonally induced activation of previously existing, reversibly deactivated enzyme. The activation is not a direct allosteric effect of indoleacetic acid or sugars. It is blocked by inhibitors of energy metabolism, by 2-deoxyglucose, and by high osmolarity, but not by Ca(2+) at concentrations that inhibit auxin-induced elongation and prevent promotion of sugar uptake by indoleacetic acid, and not by alpha, alpha'-dipyridyl at concentrations that inhibit formation of hydroxyproline. Regulation of the system could be due either to an ATP-dependent activating reaction affecting this enzyme, or to changes in levels of a primer or a lipid cofactor.

The mitogenic effect of lipopolysaccharide on bone marrow-derived mouse lymphocytes. Lipid A as the mitogenic part of the molecule

Lipopolysaccharides with different structure, isolated from different mutant strains of Escherichia coli and Salmonella bacteria, and chemical degradation products of these lipopolysaccharides have been employed to investigate which part of the lipopolysaccharide molecule exerts mitogenic effects on bone marrow-derived mouse lymphocytes. Within the structure of lipopolysaccharide consisting of lipid A, a core polysaccharide, and the O-polysaccharide antigen, lipid A was found to be the mitogenic part. The mitogenic effect of lipid A, consisting of phosphorylated glucosamine disaccharide units with ester- and amide-linked fatty acids, was lost after alkali treatment, which removes ester-linked fatty acids. Insertion of the lipid A portion of lipopolysaccharides into the lipid bilayer of the plasma membranes of bone marrow-derived lymphocytes is discussed as the initial mitogenic action.

The Structure of Plant Cell Walls: III. A Model of the Walls of Suspension-cultured Sycamore Cells Based on the Interconnections of the Macromolecular Components

Degradative enzymes have been used to obtain defined fragments of the isolated cell walls of suspension-cultured sycamore cells. These fragments have been purified and structurally characterized. Fragments released from endopolygalacturonase-pretreated cell walls by a purified endoglucanase and the fragments extracted from these walls by urea and alkali provide evidence for a covalent connection between the xyloglucan and pectic polysaccharides. Fragments released by a protease from endopolygalacturonase-endoglucanase-pretreated cell walls provide evidence for a covalent connection between the pectic polysaccharides and the structural protein of the cell wall. Based on these interconnections and the strong binding which occurs between the xyloglucan and cellulose, a tentative structure of the cell wall is proposed.

The transfer of mannose from guanosine diphosphate mannose to dolichol phosphate and protein by pig liver endoplasmic reticulum

When pig liver microsomal preparations were incubated with GDP-[(14)C]mannose, 10-40% of the (14)C was transferred to mannolipid and 1-3% to mannoprotein. The transfer to mannolipid was readily reversible and GDP was one of the products of the reaction. It was possible to reverse the reaction by adding excess of GDP and to show the incorporation of [(14)C]GDP into GDP-mannose. When excess of unlabelled GDP-mannose was added to a partially completed incubation there was a rapid transfer back of [(14)C]mannose from the mannolipid to GDP-mannose. The other product of the reaction, the mannolipid, had the properties of a prenol phosphate mannose. This was illustrated by its lability to dilute acid but stability to dilute alkali, and by its chromatographic properties. Dolichol phosphate stimulated the incorporation of [(14)C]mannose into both mannolipid and into protein, although the former effect was larger and more consistent than the latter. The incorporation of exogenous [(3)H]dolichol phosphate into the mannolipid, and its release, accompanied by mannose, on treatment of the mannolipid with dilute acid, confirmed that exogenous dolichol phosphate can act as an acceptor of mannose in this system. It was shown that other exogenous polyprenol phosphates (but not farnesol phosphate or cetyl phosphate) can substitute for dolichol phosphate in this respect but that they are much less efficient than dolichol phosphate in stimulating the transfer of mannose to protein. Since pig liver contained substances with the chromatographic properties of both dolichol phosphate and dolichol phosphate mannose, which caused an increase in transfer of [(14)C]mannose from GDP-[(14)C]mannose to mannolipid, it was concluded that endogenous dolichol phosphate acts as an acceptor of mannose in the microsomal preparation. The results indicate that the mannolipid is an intermediate in the transfer of mannose from GDP-mannose to protein. Some 4% of the mannose of a sample of mannolipid added to an incubation was transferred to protein. A scheme is proposed to explain the variations with time in the production of radioactive mannolipid, mannoprotein, mannose 1-phosphate and mannose from GDP-[(14)C]mannose that takes account of the above observations. ATP, ADP, UTP, GDP, ADP-glucose and UDP-glucose markedly inhibited the transfer of mannose to the mannolipid.

Conservation and transformation of energy by bacterial membranes

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