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At least 1,765 records · Page 98Linked to original sources
PubMed1988

Structure of light-harvesting chlorophyll a/b protein complex from plant photosynthetic membranes at 7 A resolution in projection.

The structure of thin three-dimensional crystals of the light-harvesting chlorophyll a/b protein complex, an integral membrane protein from the photosynthetic membrane of chloroplasts, has been determined at 7 A (1 A = 0.1 nm) resolution in projection. The structure analysis was carried out by image processing of low-dose electron micrographs, and electron diffraction of thin three-dimensional crystals preserved in tannin. The three-dimensional crystals appeared to be stacks of two-dimensional crystals having p321 symmetry. Results of the image analysis indicated that the crystals were disordered, due to random translational displacement of stacked layers. This was established by a translation search routine that used the low-resolution projection of a single layer as a reference. The reference map was derived from the symmetrized average of two images that showed features consistent with the projected structure of negatively stained two-dimensional crystals. The phase shift resulting from the displacement of each layer was corrected. Phase shifts were then refined by minimizing the phase residual, bringing all layers to the same phase origin. Refined phases from different images were in agreement and reliable to 7 A resolution. A projection map was generated from the averaged phases and electron diffraction amplitudes. The map showed that the complex was a trimer composed of three protein monomers related by 3-fold symmetry. The projected density within the protein monomer suggested membrane-spanning alpha-helices roughly perpendicular to the crystal plane. The density in the centre and on the periphery of the trimeric complex was lower than that of the protein, indicating that this region contained low-density matter, such as lipids and antenna chlorophylls.

Chlorophyll↗
PubMed1989

Two-dimensional structure of plant light-harvesting complex at 3.7 A [corrected] resolution by electron crystallography.

The structure of the light-harvesting chlorophyll a/b-protein complex has been determined at 3.7 A resolution in projection by electron diffraction, electron microscopy and image analysis. Diffraction patterns and high-resolution spotscan images of two-dimensional crystals stabilized with tannin were recorded at low temperature. Phases of structure factors were obtained directly by image processing, after correction of the images for lattice distortions, defocus and beam tilt. Amplitudes were measured by electron diffraction. The projection map shows the detailed structure of the trimeric complex, suggesting the positions of two domains of potential structural and functional homology, of one membrane-spanning alpha-helix approximately perpendicular to the membrane plane and of several tightly bound lipid molecules.

Chlorophyll↗
PubMed1988

Antimutagenesis by factors affecting DNA repair in bacteria.

The term 'antimutagen' was originally used to describe an agent that reduces the apparent yield of spontaneous and/or induced mutations, regardless of the mechanisms involved. The 'antimutagens' include 'desmutagens' and 'bio-antimutagens'. In this article, our attention was focused on the bio-antimutagens affecting DNA repair in bacteria. Cobaltous chloride reduced the frequency of mutations in Escherichia coli induced by MNNG. The possibility that metal compound inhibits the growth of mutagen-treated cells was examined. The results clearly showed that the antimutagen surely reduces the mutation rate. The target of cobaltous chloride was found to be cellular factors including Rec A. Vanillin and cinnamaldehyde had strong antimutagenic activities against UV, 4NQO and AF-2. They stimulated Rec A-dependent recombination repair functions in the mutagen-treated cells. Among plant materials, tannins possess antimutagenic activity against UV-induced mutations in E. coli. It has been found that tannic acid stimulates the excision repair encoded by the uvrA gene thereby reducing the yield of mutants. Substances which are antimutagenic in bacterial systems also had antimutagenic activity in cultured mammalian cell systems. Vanillin reduced the frequency of mutagen-induced chromosomal aberrations.

Bacteria↗
PubMed1989

Crude tea extracts decrease the mutagenic activity of N-methyl-N'-nitro-N-nitrosoguanidine in vitro and in intragastric tract of rats.

The effects of tea extracts and their ingredients, catechins and L-ascorbic acid (AsA), on the mutagenicity of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were examined in vitro and in the stomachs of rats using E. coli WP2 and S. typhimurium TA100. The extracts of green tea and black tea leaves decreased the mutagenic activity of MNNG to E. coli WP2 in vitro in a desmutagenic manner. Catechins such as (-)-epigallocatechin from green tea leaves and the low-molecular-weight tannin fraction isolated from black tea extract with HP-20 resin also exhibited inhibitory effects against the mutagenic activity of MNNG. A desmutagenic effect of AsA on MNNG-induced mutagenicity was observed depending on the dose, though it was complicated. The effects were also demonstrated in the stomachs of rats by assaying the bacterial mutagenic in vitro; the tea extracts previously given orally to rats reduced the mutagenic activity of MNNG remarkably, though simultaneous administration showed less effect. The effectiveness of tea extracts for the decrease of MNNG-induced mutagenesis in vitro and in vivo suggests that the habitual drinking of tea may reduce the tumor-initiating potency of MNNG-type nitrosoureido compounds if they are formed in the stomach.

Animals↗
PubMed1993

Mutagenicity of chemicals added to foods.

Much attention has recently been brought to the fact that many natural components of the diet are mutagenic and/or carcinogenic. Approximately 2700 distinct chemical entities, chemical mixtures, and plant extracts are allowed as direct food additives by the US F.D.A. These include chemicals found in the body, natural components of foods, and synthetic chemicals. In addition to the chemicals among these additives that are mutagenic, there are a number of mutagens that are normally present in the plant products that are consumed as part of the normal diets. The mutagenicity in Salmonella of these food additives was identified using the National Toxicology Program and US E.P.A. Gene-Tox databases. Relatively few of the chemicals deliberately added to foods have been tested for mutagenicity. Among the chemicals tested, approximately 15% were mutagenic in Salmonella. The mutagens include both organic and inorganic substances. Many of the natural plant components, such as flavonoids, hydrazides, and tannins also have been shown to be mutagenic. However, these natural components are not considered as food additives. A large proportion of the mutagenic food additives appear to act through the generation of oxygen- or free radicals. Although the relationships between mutagenicity and carcinogenicity of electrophilic chemicals has been well studied, the potential hazard of low-level increases in free-radical generating substances on tumor incidences is unknown.

Animals↗
PubMed1996

A benzoic acid glycoside from Geniostoma antherotrichum.

Fractionation of an HIV-inhibitory organic extract of Geniostoma antherotrichum afforded a glycoside derivative, which has been characterized as 2-hydroxy-3-O-beta-D-glucopyranosyl-benzoic acid (1) on the basis of spectral analyses. The HIV-inhibitory activity of the extract was traced to polymeric tannins, while 1 was found to be inactive in the National Cancer Institute's primary anti-HIV screen.

Antiviral Agents↗
PubMed1986

Hemolytic activity in crude polysaccharide extracted from grain sorghum [Sorghum bicolor (L.) Moench].

A crude polysaccharide that hemolyzed human red blood cells of the ABO types was isolated from the condensed tannin fraction of Sorghum bicolor. It contained primarily 2-hydroxybenzoic acid and glucose and had a molecular weight of greater than 6000. Limit hemolytic activity for each of four blood group cells corresponded to a range of 110-27 micrograms of carbohydrate per assay.

Edible Grain↗
PubMed1992

Plants with a reputation against snakebite.

Many plants are recommended in traditional medicine as active against various effects of snakebite. Few attempts have been made to investigate the veracity of these assertions in controlled experiments. Several workers, mainly Oriental, have investigated the reputation of such plants by performing in vitro and in vivo experiments in order to demonstrate whether there was any protective effect, using drugs or mixtures of drugs prepared using traditional formulae. In some studies, these extracts were administered to mice before or after treatment with different elapid or crotalid venoms. Other papers deal with selected compounds isolated from Schumanniophyton magnificum, Eclipta prostrata or Aristolochia shimadai, and their capacity to inhibit phospholipase A2 or other enzymes (e.g. ATPase) or for physiological and biochemical properties (such as effects on uterine tone or the protection of mitochondrial membranes). Japanese workers have described the antihaemorrhagic effect of persimmon tannin from Diospyros kaki. Atropine has been attributed a life-prolonging effect after black mamba venom treatment. Prolonged survival was also observed after pretreatment with extracts of Diodia scandens and Andrographis paniculata. Some authors have found little or no beneficial effects. The papers collected so far show that there are no systematic investigations in this field.

Animals↗
PubMed1984

The influence of pH on the convertogenic activity of plant phenolics.

The genotoxicity of plant phenolics, including pyrogallol, gallic acid, resorcinol and catechin, and a water extract and tannin fraction of betel nut (Areca catechu) was examined at pH levels ranging from 5 to 10. Strain D7 of Saccharomyces cerevisiae was used since the cells can withstand a wide range of pH levels without any loss of viability. At alkaline pH ranges, the examined phenolics and betel nut extracts induced mitotic conversion, whereas they lacked this capacity at acid pH levels. This phenomenon may be due to the rapid autoxidation of phenolics under alkaline conditions, which leads to the generation of H2O2 and free radicals. The results indicate that plant phenolics may pose a genotoxic hazard during chewing of lime-containing betel quid and tobacco which causes the salivary pH to rise above 8.

Areca↗
PubMed1993

In vitro activity of a Combretum micranthum extract against herpes simplex virus types 1 and 2.

The authors demonstrate in vitro antiviral activity of a methanolic extract of Combretum micranthum leaves against HSV-1 and HSV-2. This activity is present only in the extract dissolved 7 days before the assay, but not in the freshly prepared extract, thus indicating the presence of inactive precursors which undergo spontaneous transformations into active compounds. The alkaline autooxidation of the methanolic extract promotes this rapid transformation. The precursors have been identified as condensed catechinic tannins, which, under alkaline conditions, suffer rapid cleavage, intramolecular rearrangement to catechinic acid and autooxidation. The alkaline autooxidation products of the methanolic extract of C. micranthum and those of the synthetic catechinic acid show similar I.R. and U.V. absorption curves, as well as similar anti-HSV-1 and -HSV-2 activities. EC50s of catechinic acid autooxidation products against HSV-1 and HSV-2 replication were 2 micrograms/ml and 4 micrograms/ml, respectively, when cell cultures were treated with the compound during virus infection.

Animals↗
PubMed1990

Cytological observations on spruce needles after prolonged treatment with ozone and acid mist.

Light and electron microscopic studies of four clones of 5-year-old Picea abies trees subjected to ozone and acid mist treatment showed, that: (1) Clones respond differently to the treatment, with clone 14 the most sensitive clone. (2) Main effects were observed in the mesophyll; the vascular strand showed minor cellular changes. (3) Needle shape and ratio of intercellular area to cross section was clone- age-dependent, with a clear increase in intercellular space associated with the treatment (clone 14 and 11 only). (4) Accumulation of tannins in vacuoles was clone-specific. (5) Strong starch formation was found in all samples; in clones 14 and 133 this formation was enhanced by the treatment in older needles, if number of starch grains per cell was calculated. (6) The accumulation of plastoglobules in plastids depended on clone and age, with the older needles containing more globules. In clones 11 and 133, the treatment led to an increase in the number of plastoglobules. (7) Grana stacking in all clones and both needle ages subjected to ozone and acid mist was significantly reduced. The observed changes in the ultrastructure of needle tissue are comparable to those found in field investigations with similar conditions, or phytotron studies evaluating pollution effects on spruce trees.

Journal Article↗
PubMed1993

Inhibitory effects of semisynthetic flavonoid derivatives on the biochemical markers of tumor promotion in mouse epidermis in vivo.

Two sets of flavonoid derivatives were synthesized from condensed tannins (CTs) or catechin, and compared with the procyanidin monomer models, (+)-catechin and (-)-epicatechin, for their abilities to inhibit the biochemical effects of the potent tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) in mouse epidermis in vivo. Topical applications of the semisynthetic flavonoids, catechin dialkyl ketals and epicatechin-4-alkylsulphides inhibit TPA-induced ornithine decarboxylase (ODC) activity to a much greater degree than catechin or epicatechin. Moreover, they reduce TPA-stimulated hydroperoxide (HPx) production, a response that cannot be inhibited by catechin or epicatechin. These compounds also inhibit the sequential stimulations of protein and DNA synthesis linked to TPA promotion. The remarkable effectiveness of these synthetic compounds, especially against the ODC marker of skin tumor promotion, suggests that they may be effective anti-tumor promoters.

Animals↗
PubMed1982

Guaraná (Paullinia cupana var. sorbilis): ecological and social perspectives on an economic plant of the central Amazon basin.

Guaraná is considered an ideal crop for supplementing the incomes of small peasant farmers in the Amazon basin. A fast-growing perennial, guaraná can be planted in the midst of manioc crops, allowing the formation of extensive orchards in the place of regenerating scrub once the manioc has been harvested. Traditional forms of guaraná agriculture practised by the Saterê-Mawé Indians compare favourably with the plantation system favoured by government agronomists. Indigenous techniques of hand-processing guaraná are also shown to produce better quality in the finished product than those practices adopted by industrial concerns. A detailed comparison of two systems of production show the Indians' implicit concern to avoid oxidization of the phenolic compounds in the seed, since this leads to the guaraná becoming dark in colour, bitter in taste, and irritating to the gastrointestinal tract. The short-term medicinal effects of guaraná are commonly thought to result from a high content of caffeine and associated alkaloids, as well as from considerable amounts of tannin. Future research may well show that various saponins also play an important part in the drug's pharmacology, particularly with regard to its long-term influence as a general tonic and prophylactic.

Agriculture↗
PubMed1983

The chewing of khat in Somalia.

Khat (Catha edulis Forsk.), known in Somalia as "qaad" or "jaad", is a plant whose leaves and stem tips are chewed for their stimulating effect. From the Harar area, khat has been introduced at different times into the present day territories of Somalia, Djibouti, South and North Yemen, Kenya, Madagascar, Tanzania and down to south eastern Africa. The plant, which belongs to the Celestraceae family, grows wild at altitudes of 1500-2000 m above sea level. Among the various compounds present in the plant (more than forty alkaloids, glycosides, tannins, terpenoids, etc.), two phenylalkylamines, namely cathine [+)-norpseudoephedrine) and cathinone [-)S-o-aminopropiophenone) seem to account mostly for the effect. The consumers get a feeling of well-being, mental alertness and excitement. The after effects are usually insomnia, numbness and lack of concentration. The excessive use of khat may create considerable problems of social, health and economic nature. These problems have been summarily reviewed. Khat chewing started at different times in different parts of Somalia. Since World War II, the prevalence of the practice has continuously increased and no social group is excluded. An epidemiological research to compare Northern and Southern regions of Somalia and to obtain a rough estimate of prevalence, definition of social characteristics of the groups of consumers, specification of the motivations, patterns of use and effects during and after consumption has been conducted. Consumers and non-consumers (7485 people) were randomly interviewed in the two regions. Khat consumption in relation to sex, age, occupation and grade of education is presented.

Adolescent↗
PubMed1986

Hypotensive effect of Rhamnus lycioides extracts.

Intravenous administration of a lyophilized hot water extract and various organic solvent extracts of Rhamnus lycioides to normotensive anesthetized Wistar rats produced a lowering of systemic arterial blood pressure. Acute toxicity of the lyophilized extract was studied in mice by intraperitoneal injection. The phytochemical analyses revealed the presence of steroids-triterpenes, catechin tannins, flavonoids, sugars and resins.

Animals↗
PubMedDate not supplied

Responses of gastrointestinal smooth muscle preparations to a muscarinic principle present in Sida veronicaefolia.

The effects of the water-soluble fraction from an alcoholic extract of Sida veronicaefolia leaves were studied on isolated guinea-pig ileum and isolated rabbit duodenum. Agonist/antagonist studies, using atropine, hexamethonium and mepyramine, suggest that the active principle may be muscarine-like. Preliminary biochemical investigations on the extract showed negative results for the presence of alkaloids, saponins and true tannins, but confirmed the presence of pseudotannins, oligosaccharides, flavonoids, choline, fructose, peptides, histidine, glycine, tyrosine, oxalic acid and phenolic acid.

Animals↗
PubMed1989

Traditional antileukodermic herbal remedies in the Mediterranean area.

More than 100 antileukodermic recipes, involving about 80 plant species used in Italy through the centuries, were collected from Renaissance texts, folk medicine and contemporary herbal usage. The possible efficacy of the recorded plants in stimulating physiological skin pigmentation is discussed in the light of present phytochemical and pharmacological knowledge. Many plants contain erythemogenic substances, some of which (furocoumarins, hypericin) induce light-mediated hypermelanogenesis. Other plants can colour the epidermal keratin (tannins, anthraquinones) or the subcutaneous fat depot (beta-carotene). The usefulness of other plants remains obscure.

Humans↗
PubMed1989

Chemical and pharmacological studies on Talauma ovata St. Hil. (Magnoliaceae).

Antidiabetic activity of crude extract of leaves of Talauma ovata St. Hil. (Magnoliaceae) was analysed as part of a general pharmacological screening of this plant. Chemical analysis demonstrated the presence of phytosteroids, saponins, alkaloids and tannins in the crude extract. Pharmacological studies failed to demonstrate hypoglycemic effect of this plant in normoglycemic, hyperglycemic or alloxan-diabetic rats. The low LD50 obtained for this plant strongly suggests that its consumption by the population may be hazardous.

Animals↗