Macromolecular distribution of Acacia senegal gum (gum arabic) by size-exclusion chromatography

Fractionation of Acacia senegal gum has been carried out on Sephacryl gels S-400 and S-500. The shape and relative height of the chromatograms are sample dependent.Physicochemical data including circular dichroism and the weight-average molecular weights distribution show that about 70% of the material is composed of homogeneous polysaccharide chains with a very low nitrogen content. The remaining material is a combination of polysaccharide and nitrogen moieties (probably an arabinogalactan-protein complex).Our data are consistent with the new and simplified structural models proposed recently for this polysaccharide.     

Interfacial rheology of surface-active biopolymers: Acacia senegal gum versus hydrophobically modified starch

Acacia gum is a hybrid polyelectrolyte containing both protein and polysaccharide subunits. We study the interfacial rheology of its adsorption layers at the oil/water interface and compare it with adsorbed layers of hydrophobically modified starch, which for economic and political reasons is often used as a substitute for Acacia gum in technological applications. Both the shear and the dilatational rheological responses of the interfaces are considered. In dilatational experiments, the viscoelastic response of the starch derivative is just slightly weaker than that for Acacia gum, whereas we found pronounced differences in shear flow: The interfaces covered with the plant gum flow like a rigid, solidlike material with large storage moduli and a linear viscoelastic regime limited to small shear deformations, above which we observe apparent yielding behavior. In contrast, the films formed by hydrophobically modified starch are predominantly viscous, and the shear moduli are only weakly dependent on the deformation. Concerning their most important technological use as emulsion stabilizers, the dynamic interfacial responses imply not only distinct interfacial dynamics but also different stabilizing mechanisms for these two biopolymers.     

Specific leaf mass, fresh: dry weight ratio, sugar and protein contents in species of Lamiaceae from different light environments

Samples from eleven species of Lamiaceae were collected from different light environments in Venezuela for laboratory analysis. The studied species were: Plectranthus scutellarioides (Ps), Scutellaria purpurascens (Sp), Hyptis pectinata (Hp)), H. sinuata (Hs). Leonorus japonicus (Lj), Plecthranthus amboinicus (Pa) Ocimum hasilicum (Ocb), O. campechianum (Occ) Origanum majorana (Orm), Rosmarinus officinali, (Ro) and Salvia officinalis (So). Protein and soluble sugar contents per unit of area were measured, Specific Leaf Mass (SLM) and fresh:dry weight (FW/DW) ratios were calculated. The higher values for soluble sugars contents were present in sun species: Lj, Pa, Ocb, Occ, Orm, Ro and So; the lower values were obtained in low light species: Ps, Sp, Hp, Hs. The values of protein content do not show any clear trend or difference between sun and shade environments. The lowest values for the fresh weight: dry weight ratio are observed in sun species with the exception of Lj and Pa, while the highest value is observed in Pa, a succulent plant. The higher values of specific leaf mass (SLM) (Kg DMm(-2)) are observed in sun plants. The two way ANOVA revealed that there were significant differences among species and between sun and low light environments for sugar content and FW:DW ratio. while SLM was significant for environments but no significant for species, and not significant for protein for both species and environments. The soluble sugar content, FW:DW ratio and SLM values obtained in this work, show a clear separation between sun and shade plants. The sugar content and FW:DW ratio are distinctive within the species, and the light environment affected sugar content. FW:DW ratio and SLM. These species may he shade-tolerant and able to survive in sunny environments. Perhaps these species originated in shaded environments and have been adapting to sunny habitats.     

Nitrogen metabolism inErica and soybean,two species differing by their sensitivity to inorganic N source

Growth of soybean was not altered, whatever the inorganic N-source (NO₃, NH₄ or a NO₃/NH₄ mixture); conversely, growth of Erica x darleyensis plants in vitro decreased more in. NH₄ medium than in a NO₃ medium, compared to a NO₃/NH₄ medium. The GS/GOGAT pathway (in NH₄ medium), the nitrate and nitrite reductase activities (in NO₃ medium), as the contents in free nitrogenous forms and total nitrogen (in NO₃ and NH₄ media) were not more altered in Erica than in soybean, compared to a NO₃/NH₄ medium. PEPCase activity was the highest in soybean irrespective of the N-treatments; the involvement of PEPCase in N-metabolism could be explained by its function in ionic and osmotic balances rather than its function in supplying carboxylates as acceptors for NH₄-assimilation.     

The population of Acacia tree species producing gum arabic in the Karamoja region, Uganda

The study aimed at determining the population status of the different Acacia tree species producing gum arabic in the undisturbed, grazed and cultivated habitats in the Karamoja region, Uganda. A total of 135 sample plots each measuring 20 × 20 m² (0.04 ha) with each habitat having 45 plots were selected and established in the seven counties using a simple random sampling technique. The tree species present, their abundances and sizes were recorded. Twelve Acacia species were identified and a total of 5535 recorded in the sampled area. Out of these, five were gum‐producing acacias. Acacia senegal dominated the acacias in all the seven counties and in all habitats of Karamoja with Acacia nilotica (72.3%), Acacia seyal (13.4%), Acacia sieberiana (4%) and Acacia gerrardii (2.6%). Non‐gum‐producing acacias constituted 7.19% of the total abundance. The tree densities increased with increase in tree size in the undisturbed and grazed habitats but decreased in the cultivated habitat. Most Acacia trees were of large size, an indication of old age and poor regeneration that could affect their future population status. It is recommended that further investigations be carried out into the causes of poor regeneration of Acacia species.     

Acacia gum and its use by bushbabies,Galago senegalensis (Primates: Lorisidae)

Lesser bushbabies (Galago senegalensis moholi)were studied by radiotracking over a 2-year period (August 1975 to August 1977)at a thornveld study site in the Northern Transvaal, South Africa. It was confirmed that the diet consisted exclusively of plant exudates (gums) and arthropods;available fruits were never eaten. The gums were taken from the trunks and branches of Acaciatrees, particularly from Acacia karroo(the major source), from A. tortilis,and to a small extent from A. nilotica.Chemical analysis shows that gums consist predominantly of carbohydrates and water, with small quantities of fiber, protein, and minerals (notably calcium, magnesium, and potassium). Thus, the gums probably present first and foremost a source of carbohydrate in the diet of the lesser bushbaby, though it seems likely that special mechanisms must exist for digestion of the polymerized pentose and hexose sugars. The calcium content of the gums (approx. 1% by weight) is probably significant in offsetting the low calcium content of the arthropod prey, and their high calcium:phosphorus ratio may well counterbalance the low calcium:phosphorus ratio of the arthropods. The gums are apparently produced largely in response to insect activity. Larvae of beetles (families Cerambycidae,Buprestidae, and Elateridae) and of moths (family Coccidae) bore channels beneath the tree surface, and gum is liberated through apertures made during invasion of the host Acacia.Fly larvae (family Odiniidae) may also develop in the gumfilled cavities. Gum exuding onto the surface is collected by the bushbabies on regular nightly visits, and firm evidence was obtained, in the form of characteristic marks on trap baseboards and certain gum sites, that the toothscraper in the lower jaw is used to scoop away gum from tree surfaces. Foraging for, and feeding upon, gum increased during the winter months, which may be particularly harsh in certain years. In the especially cold winter covered by the study, insect availability was minimal and the lesser bushbabies fed mainly on gum, with some of them reducing their total activity period during the night. Gums are available throughout the year and detailed records indicated no clearcut seasonal pattern of gum production. They are therefore an important yearround food resource for the lesser bushbabies. Feeding on gums has been reported for a wide range of primate species in recent years (especially for various species of the families Cheirogaleidae, Lorisidae, and Callitrichidae), and these plant exudates must now be regarded as an important dietary category within the order Primates.     

Fractionation of low molecular weight heparin species and their interaction with antithrombin.

Preparations of low molecular weight porcine heparin with an average specific anticoagulant activity of 94 units/mg were fractionated into "active" and "relatively inactive" forms of the mucopolysaccharide of approximately 6000 daltons each. The active fraction was further subdivided into various species with descending but significant affinities for the protease inhibitor as well as decreasing but substantial anticoagulatn potencies. "Highly active" heparin (approximately 8% of the low molecular weight pool) possesses a specific anticoagulant activity of 350 +/- 10 units/mg. The relatively inactive fraction (67% of the low molecular weight pool) exhibits a specific anticoagulant activity of 4 +/- 1 units/mg. The binding of highly active heparin to antithrombin is accurately described by a single-site binding model with a KHep-ATDISS of approximately 1 X 10(-7) M. Variations in this binding parameter secondary to changes in environmental variables indicate that charge-charge interactions as well as an increase in entropy are critical to the formation of the highly active heparin-antithrombin complex. The interaction of relatively inactive heparin with the protease inhibitor is characterized by an apparent KHep-ATDISS of 1 X 10(-4) M. In large measure, this is due to small amounts of residual active mucopolysaccharide (0.5%). The ability of the highly active heparin to accelerate the thrombin-antithrombin interaction was also examined. We were able to demonstrate that the mucopolysaccharide acts as a catalyst in this process and is able to initiate multiple rounds of enzyme-inhibitor complex formation. The rate of enzyme neutralization is increased to a maximum of 2300-fold as the concentration of heparin is raised until the inhibitor is saturated with mucopolysaccharide. Further increases in heparin concentration result in a reduction in the speed of enzyme neutralization. This appears to be due to the formation of thrombin-heparin complexes. A mathematical model is given which provides a relationship between the initial velocity of enzyme neutralization and reactant concentrations.     

Characterization and application of a new aqueous two phase system based on gum acacia (ex.Acacia senegal), a naturally occuring polysaccharide,and polyethylene glycol

Summary Gum acacia has been used with polyethylene glycol to form a two phase aqueous polymeric system. The system followed Newtonian fluid behaviour and the acacia rich phase supported a high concentration of protein (>1.3 mg/ml) in solution. The data on partitioning of various proteins in this system indicates that it can be used for selective separation of a particular protein from a protein mixture.     

The content of protein,fibre and minerals of leaves of selected Acacia species indigenous to north-western Tanzania

Abstract

Browse tree leaves of six species of Acacia (A. angustissima L., A. drepanolobium L., A. nilotica L., A. polyacantha L., A. senegal L., A. tortilis L.) were screened for chemical composition, including minerals and trace elements. Crude protein (CP) varied among the species from 145 (A. senegal) to 229 g/kg DM (A. angustissima). The species had moderate to high levels of minerals. The concentrations of Ca, P, Mg and S varied among the species from 14.6 – 31.5, 3.5 – 4.9, 1.4 – 3.0 and 1.7 – 2.8 g/kg DM, respectively. The forages showed relatively low concentrations of trace elements. Content of trace elements varied among the species from 4.5 – 23.8, 99.4 – 173.6, 146.2 – 432, 41.0 – 90.1, 10.9 – 22.2 and 0.05 – 0.65 mg/kg DM for Cu, Mo, Fe, Mn, Zn and Co, respectively. All leaves of browse species would meet the normal requirements for Ca, P, Mg and S in ruminants, although some species had higher levels of Ca than tabulated mineral requirements in livestock. Assayed Cu, Mn, Zn and Co would satisfy the lower range of recommended requirements of trace elements depending on their bioavailability. Therefore, browse leaves from Acacias could form good sources of CP and mineral supplements to ruminants.     

The content of protein, fibre and minerals of leaves of selected Acacia species indigenous to north-western Tanzania

Browse tree leaves of six species of Acacia (A. angustissima L., A. drepanolobium L., A. nilotica L., A. polyacantha L., A. senegal L., A. tortilis L.) were screened for chemical composition, including minerals and trace elements. Crude protein (CP) varied among the species from 145 (A. senegal) to 229 g/kg DM (A. angustissima). The species had moderate to high levels of minerals. The concentrations of Ca, P, Mg and S varied among the species from 14.6-31.5, 3.5-4.9, 1.4-3.0 and 1.7-2.8 g/kg DM, respectively. The forages showed relatively low concentrations of trace elements. Content of trace elements varied among the species from 4.5-23.8, 99.4-173.6, 146.2-432, 41.0-90.1, 10.9-22.2 and 0.05-0.65 mg/kg DM for Cu, Mo, Fe, Mn, Zn and Co, respectively. All leaves of browse species would meet the normal requirements for Ca, P, Mg and S in ruminants, although some species had higher levels of Ca than tabulated mineral requirements in livestock. Assayed Cu, Mn, Zn and Co would satisfy the lower range of recommended requirements of trace elements depending on their bioavailability. Therefore, browse leaves from Acacias could form good sources of CP and mineral supplements to ruminants.     

Emulsifying behaviour of gum arabic. Part 2: Effect of the gum molecular weight on the emulsion droplet-size distribution

The effect of the molecular weight of the gum arabic sample on droplet-size distributions of n-hexadecane-in-water emulsions (1% wt gum, 10% vol. oil) has been investigated at neutral pH. A high-molecular-weight fraction (0·87% nitrogen) corresponding to 10% of a natural gum (0·38% N) gives initially slightly larger droplets but better emulsion stability than the low-molecular-weight fraction (0·35% N) corresponding to the residual 90% of the original gum. Samples of a different gum arabic (0·35% N) subjected to different degrees of controlled degradation give decreasing emulsion stability with reduction in weight-average molecular weight from 3·1 × 10⁵ to 2·2 × 10⁵Da.     

Mature rat testis contains a high molecular weight species of phosphatidylinositol transfer protein

Immunoblot analysis of a rat testis cytosol fraction revealed two proteins which reacted with a polyclonal rabbit antibody to bovine phosphatidylinositol transfer protein. These two proteins were separated by anion exchange and molecular sieve column chromatographic procedures and shown to catalyze the transfer of phosphatidylinositol and phosphatidylcholine between populations of small unilamellar vesicles. One protein was identified as the phosphatidylinositol transfer protein detectable in 16 other rat tissues and many eukaryotic species; the other phosphatidylinositol transfer protein was unique to testis. The molecular masses of the proteins, determined under denaturing electrophoretic conditions, were 35 and 41 kDa, respectively. When testis was examined in animals from birth to six weeks of age, the 35-kDa protein was present throughout, while the 41-kDa protein first appeared during week 4 and increased to adult levels by week 6; a small yet significant increase in tissue phosphatidylinositol transfer activity accompanied this expression of the testis-specific protein. Selective destruction of Leydig cells by ethylene dimethanesulfonate did not cause any detectable loss of the 41-kDa phosphatidylinositol transfer protein. The structural and catalytic relationships between the two testicular phosphatidylinositol transfer protein species remain to be elucidated.     

Root growth and lignification of two wheat species differing in their sensitivity to NaCl, in response to salt stress

Application of a 100-mM NaCl salt stress to wheat seedlings of a salt-tolerant (Triticum durum var. Ben Béchir) and a salt-sensitive (Triticum aestivum var. Tanit) species decreases the fresh and dry weights of roots especially in the salt-sensitive species, and slightly increases the ratio of dry to fresh weight, especially in the salt-resistant species. All peroxidase activities are increased by salt stress, the water-soluble peroxidase activity being increased much more in the salt-sensitive than in the salt-tolerant species, while the opposite result is observed with the cell-wall peroxidase activity. Some water-soluble peroxidases have been hypothesised to have auxin oxidase activity (which might explain the effect observed on the root biomass), while the cell-wall peroxidases would be involved in lignification. Histochemical observation confirms a more intense lignification in the root cells of the salt-tolerant species compared to the sensitive species, under the effect of NaCl.     

The molecular weight ratio of monomethoxypolyethylene glycol (mPEG) to protein determines the immunotolerogenicity of mPEG proteins.

Immunotolerogenic activity of monomethoxypolyethylene glycol- (mPEG) conjugated proteins is a beneficial property in protein pharmaceutics. However, procedures for the preparation of tolerogenic mPEG proteins have not yet been defined. We prepared mPEG proteins with different mPEG contents using three proteins, hen egg lysozyme, ovalbumin and bovine gamma globulin, and their tolerogenicities to antigen-specific T and B cell responses were examined. We found the most appropriate ratio of tolerance induction to be 1.5-2.0, which is the molecular weight ratio of conjugated total mPEGs to protein. This value may assist in the preparation of tolerogenic mPEG proteins.     

Changes in photosynthesis,xanthophyll cycle,and sugar accumulation in two North Australia tropical species differing in leaf angles

Two tropical species of North Australia, Acacia crassicarpa and Eucalyptus pellita, have similar leaf size and leaf structure but different leaf angles. A. crassicarpa with near vertical leaf angle directly reduced photon absorption and leaf temperature (T _l) and had relatively high photosynthetic activity (P _max) and low xanthophyll cycle activity. In contrast, E. pellita with a small leaf angle exhibited high T _l, low P _max, and high activity of xanthophyll cycle which was useful for the dissipation of excessive energy and reduction of photoinhibition. In the dry season, contents of soluble sugars including pinitol, sucrose, fructose, and glucose in A. crassicarpa increased whereas larger amounts of only fructose and glucose were accumulated in E. pellita. Different sugar accumulation may be involved in osmotic adjustment of leaves during water stress that makes photosynthesis more efficient. The leaf angle may be critical for developing different protective mechanisms in these two tropical tree species that ensure optimal growth in the high irradiance and drought stress environment in North Australia.     

Tet repressor induction by tetracycline: a molecular dynamics, continuum electrostatics, and crystallographic study

The Tet repressor (TetR) mediates the most important mechanism of bacterial resistance against tetracycline (Tc) antibiotics. In the absence of Tc, TetR is tightly bound to its operator DNA; upon binding of Tc with an associated Mg²⁺ ion, it dissociates from the DNA, allowing expression of the repressed genes. Its tight control by Tc makes TetR broadly useful in genetic engineering. The Tc binding site is over 20 Å from the DNA, so the binding signal must propagate a long distance. We use molecular dynamics simulations and continuum electrostatic calculations to test two models of the allosteric mechanism. We simulate the TetR:DNA complex, the Tc-bound, “induced” TetR, and the transition pathway between them. The simulations support the model inferred previously from the crystal structures and reveal new details. When [Tc:Mg]⁺ binds, the Mg²⁺ ion makes direct and water-mediated interactions with helix 8 of one TetR monomer and helix 6 of the other monomer, and helix 6 is pulled in towards the central core of the structure. Hydrophobic interactions with helix 6 then pull helix 4 in a pendulum motion, with a maximal displacement at its N-terminus: the DNA interface. The crystal structure of an additional TetR reported here corroborates this motion. The N-terminal residue of helix 4, Lys48, is highly conserved in DNA-binding regulatory proteins of the TetR class and makes the largest contribution of any amino acid to the TetR:DNA binding free energy. Thus, the conformational changes lead to a drastic reduction in the TetR:DNA binding affinity, allowing TetR to detach itself from the DNA. Tc plays the role of a specific Mg²⁺ carrier, whereas the Mg²⁺ ion itself makes key interactions that trigger the allosteric transition in the TetR:Tc complex.     

Distribution of Acacia senegal (L.) Willd. (Fabaceae) in Uganda and its relationship to climatic factors

The aim of the study was to map the distribution of Acacia senegal and its infraspecific taxa in Uganda and predict its suitable range of occurrence based on climatic factors. The distribution of the infraspecific taxa was analysed for richness, diversity, turnover and reserve selection. Regression analysis was performed to understand the relationship between distribution of the species and climatic variables. Georeferenced species occurrence points were superimposed over temperature and vapour maps. Areas with highest taxa richness, diversity and turnover were mapped and found in the Lake Kyoga basin. The species shows preference for the northern region of the study area with dissimilar climatic pattern from the southern region and the superimposition supported findings. Variety kerensis exhibited narrower climatic, altitudinal and distribution range preference. Temperature seasonality, maximum temperature of warmest month, temperature annual range, mean temperatures of warmest and driest quarters had the highest coefficients of determination (r² > 0.7) hence most important in influencing species distribution. The most appropriate locations for in situ conservation and for germplasm collection to ensure maximum diversity is secured are found in Wabisi‐Wajala, Kiula, Kyalubanga, Bajo, Kasagala, Kabwika‐mujwalanganda, Maruzi, Moroto and Napak Central Forest Reserves. The study recommends ecological studies to understand status of A. senegal.