Extracellular Polysaccharide Synthesis Research Articles

Carbohydrate-binding proteins from cellular membranes of plant tissue

Proteins have been extracted from mitochondria, plasma membrane, Golgi apparatus and endoplasmic reticulum membranes isolated from growing mung bean hypocotyls. The fractions agglutinate trypsinized rabbit erythrocytes and can be classified therefore as lectins. The carbohydrate specificity of the lectin fractions differs for each membrane type. Total membrane preparations from a variety of plant and tissue types have also been shown to contain lectins. The results are discussed in relation to membrane fusion and the synthesis and transport of extracellular polysaccharides by the plant membrane systems.

The sites of synthesis and transport of extracellular polysaccharides in the root tissues of maize.

1. Subcellular fractionation of maize roots resulted in the isolation of the following enriched fractions: cell wall, dictyosome, smooth-membrane and rough-microsomal fractions. In addition, extracellular polysaccharide of the root slime was isolated. 2. Maizeseedling roots were incubated in vivo with d-[U-(14)C]glucose, and the pattern of incorporation of radioactivity into the polysaccharides of each fraction was investigated. 3. The differentiation of maize-root cells with respect to the synthesis of specific extracellular polysaccharide directly relates to the polysaccharide synthesized and transported within the membrane system of the cell. A fucose-containing polysaccharide, characteristic only of root slime, was present only in the membrane system of the root-tip region of the root. Regions of typical secondary wall development within the root were characterized by an increased incorporation of radioactivity into xylose of polysaccharide within the membrane system. 4. The incorporation of radioactivity into glucan polymers in the membrane fractions was very low in all regions of the root. Since in regions of secondary wall development greater than 60% of all radioactive incorporation was into a glucan polymer, it can be inferred that this polymer, most probably cellulose, is not synthesized or transported within the compartments of the membrane system. It is suggested that synthesis of cellulose occurs at the surface of the plasmalemma. 5. Maize-root cells contained 40 times more rough endoplasmic reticulum than dictyosome membrane. The relative specific radioactivities of each fraction indicated that polysaccharide was concentrated in the region of the Golgi apparatus, which showed a 100% increase in specific radioactivity compared with the rough endoplasmic reticulum. The Golgi apparatus can thus be regarded as a localized focal point on the synthetic and transport system of polysaccharide by the intracellular membrane compartments.

Differentiation on the basis of glucose requirements between the effects of somatomedin on protein synthesis and sulphate incorporation in embryonic chick cartilage

Extracellular glucose stimulates sulphate incorporation by embryonic chick or embryonic rat cartilage but not by 21-day old rat cartilage. In contrast glucose has little or no effect on amino acid transport or proline incorporation in any of these cartilages. Time course studies, in the presence or absence of glucose, suggest that the effect of extracellular glucose on sulphate incorporation in embryonic cartilage is due to the requirement for substrate for polysaccharide chain formation and not to a lack of an endogenous energy source. Stimulation by somatomedin of amino acid transport and incorporation in embryonic chick cartilage was independent of extracellular glucose. Glucose was required, however, for stimulation by somatomedin of sulphate incorporation. Stimulation of protein synthesis by somatomedin in the absence of glucose will result in a subsequent stimulation of sulphate incorporation if the tissue is transferred to a second medium containing glucose but no somatomedin. These results are interpreted as suggesting that in embryonic cartilage the limiting step in sulphated proteoglycan synthesis is protein synthesis in the presence of extracellular glucose but polysaccharide synthesis in the absence of glucose. They indicate that while the primary action of somatomedin is to stimulate amino acid uptake and hence incorporation, in the absence of glucose this stimulation cannot be potentiated as a stimulation of sulphate incorporation until adequate extracellular glucose is provided.

An electron microscope investigation of bacterial polysaccharide synthesis in human dental plaque

The in vivo synthesis of both intracellular and extracellular polysaccharides by bacteria in dental plaque from a variety of dietary sugars has been examined by electron microscopy and the amounts scored by visual assessment of the sections and photo micrographs. Fine particulate granules which formed extracellular polysaccharide on contact with sucrose were found associated with the periphery of the bacterial cell. It was suggested that this particulate material could be the precursor of dextran or levan. The exposure of plaque in vivo to different sugars clearly indicated that sucrose and glucose are rapidly incorporated into intracellular polysaccharide whereas maltose, fructose, lactose and sorbitol are utilized slowly or not at all. The synthesis of extracellular polysaccharide was only accomplished in quantity from sucrose and to a smaller degree from maltose. Studying the catabolism of the polysaccharides synthesized from sucrose it was shown that even after 30 min the amounts of both intracellular and extracellular polysaccharides exceeded the amounts originally in the plaque before exposure to sucrose. It was observed that occasionally the extracellular polysaccharide was concentrated in localized areas within the plaque. As it was shown that the polysaccharides were retained for periods exceeding 30 min it was speculated this extracellular polysaccharide may restrict locally the diffusion of acid produced from intracellular polysaccharides.

Synthesis of insoluble dextran and its significance in the formation of gelatinous deposits by plaque-forming streptococci

The synthesis of extracellular polysaccharides was studied in strains of streptococci known to induce plaque-formation in experimental animals. These organisms synthesized soluble and insoluble dextran and levan, and formed gelatinous “plaque-like” deposits in sucrose broth. Formation of these gelatinous deposits appeared to be dependent upon synthesis of insoluble dextran. Polysaccharide fractions extracted from the deposits possessed a higher average molecular weight and relative viscosity than soluble polymers present in culture liquors, suggesting that molecular weight is important in governing their solubility. Glucosyl acceptors known to promote synthesis of low molecular weight dextran were found to prevent the development of gelatinous deposits in sucrose broth, and these substances were found to inhibit the synthesis of insoluble dextran. Dextransucrase and levansucrase activity was detected in culture liquors, and in washed cell suspensions of the streptococcus strains studied. Enzyme preparations from culture liquors exhibited maximal dextran synthesis at pH 8, but displayed a plateau from pH 5 to 6. Approximately half of the dextran synthesized at pH 5–6 was soluble, whereas over 90 per cent of the dextran synthesized at pH 8 was insoluble. Levansucrase present in culture liquors formed maximal amounts of levan at pH 7. Preparations of cell-associated dextransucrase synthesized dextran optimally at pH 7, and predominantly insoluble polymers were formed from pH 5 through pH 8.

Variation in extracellular polysaccharide synthesis by cariogenic streptococci

Variation in extracellular polysaccharide synthesis by cariogenic streptococci

Extracellular polysaccharide synthesis by members of the genus Lactobacillus: conditions for formation and accumulation.

SUMMARY Members of the genus Lactobacillus were examined for their ability to synthesize extracellular polysaccharide from sucrose. Strains physiologically similar to L. pastorianus synthesized a glucan. Other strains liberated a complex polysaccharide which contained mannose and glucose. Variants of the glucan-producing strains occurred spontaneously and these lacked the capacity to synthesize glucan ; however, extracts of these bacilli contained glucansucrase and invertase. Manometric studies indicated that the latter enzyme functioned in the sucrose metabolism of these non-glucan producing variants.