Energy dependent accumulation

Energy-Dependent Accumulation of Iron by Isolated Rat Liver Mitochondria... 

Figure 4. Effect of increasing degree of respiratory inhibition on the energy-dependent accumulation of iron (%) and calcium (O) by rat liver mitochondria energized with ATP (23)...

Table IV. Energy-Dependent Accumulation of Iron and Calcium by Mitochondria Isolated from Reticulocytes and Various Organs of Rabbit"...

Rose, M.S., Smith, L.L. and Wyatt, I. (1976). Evidence for energy dependent accumulation of paraquat into rat lung. Nature 25, 419-423. 

Little is known of the chain of molecular events that brings the calcium from the luminal to the serosal side of the intestinal cells. Certainly calcium must enter the luminal and be excreted at the serosal side. Studies in which metabolic inhibitors were used have suggested that calcium uptake may involve an energy dependent accumulation of calcium in mitochondria and that calcium efflux at the serosal site against the chemical and electrical potential gradients is an active transport process. 

Antibiotic efflux Tetracyclines Energy-dependent efflux of accumulated drugs... 

The accumulation of a number of amino acids from the external medium seems almost irreversible in Saccharomyces cerevisiae. The first detailed study of this phenomenon concerned histidine [13]. Histidine uptake by the specific histidine permease HlPl is an energy dependent process which accumulates free and intact... 

For the internalisation of metals, many examples exist for which transport may be coupled to an energy-dependent process, of which only a few are described here. For example, the well-studied (e.g. [276]) Na+/K+ channel transports 3Na+ out and 2K+ in for each ATP molecule that is hydrolysed [242]. Mg2+ influx (but likely not efflux) is highly regulated in eukaryotes [277]. ATPases have been implicated in certain cases of Fe [278] or Zn [90] uptake by phytoplankton. Finally, although Cd internalisation by a polychaete appeared to be energy independent, accumulation was increased rather than decreased in the presence of ATPase inhibitors, suggesting that the efflux system might depend upon ATP synthesis [279]. 

The sequence of events that result in neurotransmission of information from one nerve cell to another across the s)mapses begins with a wave of depolarization which passes down the axon and results in the opening of the voltage-sensitive calcium charmels in the axonal terminal. These charmels are frequently concentrated in areas which correspond to the active sites of neurotransmitter release. A large (up to 100 M) but brief rise in the calcium concentration within the nerve terminal triggers the movement of the synaptic vesicles, which contain the neurotransmitter, towards the synaptic membrane. By means of specific membrane-bound proteins (such as synaptobrevin from the neuronal membrane and synaptotagrin from the vesicular membrane) the vesicles fuse with the neuronal membrane and release their contents into the synaptic gap by a process of exocytosis. Once released of their contents, the vesicle membrane is reformed and recycled within the neuronal terminal. This process is completed once the vesicles have accumulated more neurotransmitter by means of an energy-dependent transporter on the vesicle membrane (Table 2.3). 

Although all tetracyclines have a similar mechanism of action, they have different chemical structures and are produced by different species of Streptomyces. In addition, structural analogues of these compounds have been synthesized to improve pharmacokinetic properties and antimicrobial activity. While several biological processes in the bacterial cells are modified by the tetracyclines, their primary mode of action is inhibition of protein synthesis. Tetracyclines bind to the SOS ribosome and thereby prevent the binding of aminoacyl transfer RNA (tRNA) to the A site (acceptor site) on the 50S ri-bosomal unit. The tetracyclines affect both eukaryotic and prokaryotic cells but are selectively toxic for bacteria, because they readily penetrate microbial membranes and accumulate in the cytoplasm through an energy-dependent tetracycline transport system that is absent from mammalian cells. 

Resistance is related largely to changes in cell permeability and a resultant decreased accumulation of drug due to increased efflux from the cell by an energy-dependent mechanism. Other mechanisms, such as production of a protein that alters the interaction of tetracycline with the ribosome and enzymatic inactivation of the drug, have been reported. 

Data on the photon energy dependence of the biological effect has been accumulated fairly well with strand-break induction in plasmid DNA, and with an inactivation of the spore of a bacterium. These studies gave us many clues to understand the induction mechanism of biological effects in cells. However, for a complete understanding, research in the following areas should be highly promoted. 

A schematic of the reactions and energy levels involved in this scheme is shown in Fig. 10.5. The QRRK reaction scheme differs in several respects from Lindemann s treatment, reactions 10.99 and 10.100. The rate constant for the excitation step 10.136 is written to explicitly include the dependence on the amount of energy e — nhv transferred to C (n). The vibrational energy obtained in reaction 10.136 is assumed to be randomly or statistically distributed over s identical vibrational modes of the molecule. The rate constant kact (n,m) in reaction 10.137 is for formation of the activated complex, in which at least m quanta of vibrational energy have accumulated in a critical bond (out of the total of n). This rate constant depends on both n and m, and is derived below. 

Most results on calcium transport have been obtained using cytoplasmic membrane vesicles, which may be prepared in inside-out or right-side-out configurations. Inside-out vesicles may be obtained by the disruption of E. coli cells in a French press. These then accumulate Ca2+ in an energy-dependent fashion, provided ATP or an oxidizable substrate is available. Addition of phosphate enhances the uptake of calcium as calcium phosphate is precipitated inside the tell, thus accounting for the lack of exchangeability of the calcium.186... 

Anti-deoxyribonucleic acid autoantibodies from human and mice suffering from Lupus erythematosus can penetrate into cells and accumulate in the cell nucleus. Based on the characteristics of a mi-ON A autoantibodies, VAYISRGGVSTYYSDTVKGRFTRQKYNKRA peptide (P3), which exhibits a-helix, has been used as a vector for the intracytoplasmic and intranuclear translocation of macromolecules (Table 16.7) (Avrameas et al., 1998, 1999). P3 shares similar capabilities with Antenapedia peptide (Derossi et al., 1994), but in contrast P3 operates only at 37 °C by an energy dependent mechanism. P3 linked to a 19 lysine residue sequence (K19-P3) forms complexes with plasmid DNA. Efficient transfection of mouse 3T3 cells and hamster lung CCL39 cells were obtained with these complexes. This transfection was not impaired by the presence of serum and did not require helper molecules such as chloroquine. These observations suggest that peptides from cell specific anti-DNA autoantibodies may represent a source of peptide-based gene delivery system with different specificities. 

The temperature, or energy, dependence of the annihilation rate, or (Zeflf), has also been investigated using a positron trap. In this technique positrons are first accumulated at room temperature, and then their... 

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