Search results for "cyclic"

Enantiomeric separation of amino acids by capillary electrophoresis with α-cyclodextrin

1998

A simple method for separation of underivatized aromatic amino acid enantiomers is presented. The influence of α-cyclodextrin concentration, applied voltage and background buffer pH on the separation were investigated to achieve the best conditions of separation.

On the biochemical classification of yeast trehalases: Candida albicans contains two enzymes with mixed features of neutral and acid trehalase activi…

2009

Abstract Two enzymes endowed with trehalase activity are present in Candida albicans . The cytosolic trehalase (Ntc1p), displayed high activity in exponential phase regardless of the carbon source (glucose, trehalose or glycerol). Ntc1p activity was similar in neutral (pH 7.1) or acid (pH 4.5) conditions, strongly inhibited by ATP, weakly stimulated by divalent cations (Ca 2+ or Mn 2+ ) and unaffected in the presence of cyclic AMP. The Ntc1p activity decreased in stationary phase, except in glycerol-grown cultures, but the catalytic properties did not change. In turn, the cell wall-linked trehalase (Atc1p) showed elevated activity in resting cells or in cultures growing on trehalose or glyc…

Untersuchungen zur Biosynthese eines Cytokinins in Calluszellen von Laubmoossporophyten

1973

When callus cells derived from the sporogon of the hybrid Funaria hygrometrica x Physcomitrium piriforme are supplied with adenine-8-14C, they produce a labelled cytokinin which has the same chromatographic behavior as N6-γγ-(dimethylallyl)aminopurine. The cytokinin is the first radioactive product that can be detected in the culture medium. It is formed as long as labelled adenine is available. When callus cells are grown in an optimum culture medium containing amino acids, about 10% of the radioactivity supplied as adenine is found in the cytokinin. When the cells are grown in a medium without amino acids, the RNA-content of the cells and the total yield of cytokinin decrease, but about 1…

Use of Mechanistic Information for Adequate Metabolic Design of Genotoxicity Studies and Toxicological Interactions of Drugs and Environmental Chemic…

1995

Microorganisms as well as mammalian cells used for mutagenicity investigations have little or no activities for metabolism of premutagens and precarcinogens, i.e. of compounds ultimately leading to mutations and cancer but first requiring metabolic activation. Therefore, to such cells an exogenous activating system is added, generally the postmitochondrial supernatant fraction of the liver homogenate and a NADPH-generating system (Ames et al. 1976). In this situation enzymes requiring cofactors other than NADP(H) are unlikely to be active. Thus, this metabolic system is rather artificial. Monooxygenases are active in this system. They, for example, convert polycyclic aromatic hydrocarbons t…

Carotenoids and the Assembly of Light-harvesting Complexes

2006

Carotenoids are constitutive components of all light-harvesting complexes in plants and many such complexes in bacteria. In the crystal structures of several light-harvesting complexes, carotenoids are seen to span the lipid bilayer and connect components of the complex on both membrane surfaces and/or to mediate the interaction of transmembrane protein helices. This important stabilizing function suggests that these pigments are also actively involved in the assembly of light-harvesting complexes. Verification of this notion appears too ambitious a goal at present, as the question of how the pigment-protein complexes of the photosynthetic apparatus are assembled is still open. However, inf…

The apparent loss of tissue culture competence during leaf differentiation in yams (Dioscorea bulbifera L.)

1993

Explants taken from the leaves of yams (Dioscorea bulbifera L.) at different stages of development were cultured in vitro on a checkerboard using various combinations and/or concentrations of auxin (2,4-d) and cytokinin (6-BAP). An addition of cytokinin to the culture media was not essential for callus induction from explants derived from young leaves in the very early stages of expansion. When the leaves expanded further they required cytokinin and the requirement increased considerably during expansion. Explants taken from fully expanded leaves were no longer able to proliferate, even when extremely high concentrations of cytokinins were applied. Callus grown from highly immature leaves w…

2019

Water-soluble chlorophyll proteins (WSCP) from Brassicaceae form homotetrameric chlorophyll (Chl)–protein complexes binding one Chl per apoprotein and no carotenoids. Despite the lack of photoprotecting pigments, the complex-bound Chls displays a remarkable stability toward photodynamic damage. On the basis of a mutational study, we show that not only the presence of the phytyls is necessary for photoprotection in WSCPs, as we previously demonstrated, but also is their correct conformation and localization. The extreme heat stability of WSCP also depends on the presence of the phytyl chains, confirming their relevance for the unusual stability of WSCP.

Morphogenesis in Root Tip Meristem Cultures of Digitalis obscura L.

1987

Summary The morphogenic capacity of Digitalis obscura L. root tip meristems cultured in vitro has been studied, noting hormonal factors inducing differentiation and development of shoots as well as those promoting somatic embryogenesis. Caulogenesis was obtained with different auxin/cytokinin combinations but a high rate of shoot regeneration was induced by 0.1 or 0.5 ppm IAA and 1.0 ppm BA. Different stages of somatic embryo development were observed in media supplemented with auxins or high auxin/cytokinin ratios, although no complete plant regeneration was achieved. This is the first report known of shoot regeneration from root tips of Digitalis obscura L.

Plant regeneration from cultured leaves of Lavandula latifolia Medicus: Influence of growth regulators and illumination conditions

1989

Leaves were obtained from 4-week-old seedlings of Lavandula latifolia Medicus grown in vitro. Leaf explants were then cultured on MS medium supplemented with different concentrations and combinations of the auxins IAA or NAA with the cytokinin BA and maintained under three illumination conditions, 16h photoperiod, darkness or darkness followed by a photoperiod, to assess morphogenic responses. Irrespective of illumination conditions, bud regeneration was achieved only in media containing BA or BA/auxin combinations, with the best results being obtained in the presence of BA and 0.06 or 0.6 μM IAA or NAA. A photoperiod of 16h appeared to yield the best response in terms of bud regeneration p…

Is There an Advantage to Venlafaxine in Comparison with Other Antidepressants?

1997

The purpose of this article is to compare and contrast the benefits and limitations of antidepressant drugs. Several different classes of antidepressants are available for treatment of major depressive disorder, each with its own benefits and limitations as a result of its pharmacological profile. Tricyclic antidepressants (TCAs) and monoamine oxidase (MAO) inhibitors are effective in a large proportion of depressed patients, but their use is often limited by short- and long-term safety/tolerability problems. Selective serotonin reuptake inhibitors (SSRIs) exhibit comparable efficacy to TCAs in most patients, but may be less effective in certain patients. Additionally, SSRI use may by impac…