Adenosine triphosphate transport

ATP (Adenosine triphosphate) transports chemical energy within cells for metabolism. One molecule of ATP contains three phosphate groups, and it is produced from inorganic phosphate and adenosine diphosphate (ADP) or adenosine monophosphate (AMP). The standard amount of energy released from hydrolysis of ATP is ... 

Active Transport. Maintenance of the appropriate concentrations of K" and Na" in the intra- and extracellular fluids involves active transport, ie, a process requiring energy (53). Sodium ion in the extracellular fluid (0.136—0.145 AfNa" ) diffuses passively and continuously into the intracellular fluid (<0.01 M Na" ) and must be removed. This sodium ion is pumped from the intracellular to the extracellular fluid, while K" is pumped from the extracellular (ca 0.004 M K" ) to the intracellular fluid (ca 0.14 M K" ) (53—55). The energy for these processes is provided by hydrolysis of adenosine triphosphate (ATP) and requires the enzyme Na" -K" ATPase, a membrane-bound enzyme which is widely distributed in the body. In some cells, eg, brain and kidney, 60—70 wt % of the ATP is used to maintain the required Na" -K" distribution. 

The energy released in catabolic pathways is used in the electron-transport chain to make molecules of adenosine triphosphate, ATP. ATP, the final result of food catabolism, couples to and drives many otherwise unfavorable reactions. 

Phosphate condensation reactions play an essential role in metabolism. Recall from Section 14.6 that the conversion of adenosine diphosphate (ADP) to adenosine triphosphate (ATP) requires an input of free energy ADP -I-H3 PO4 ATP +H2O AG° — +30.6kJ As also described in that section, ATP serves as a major biochemical energy source, releasing energy in the reverse, hydrolysis, reaction. The ease of interchanging O—H and O—P bonds probably accounts for the fact that nature chose a phosphate condensation/hydrolysis reaction for energy storage and transport. 

Recent work has shown that bacteria, in common with chloroplasts and mitochondria, are able, through the membrane-bound electron transport chain aerobically, or the membrane-bound adenosine triphosphate (ATP) anerobically, to maintain a gradient of electrical potential and pH such that the interior of the bacterial cell is negahve and alkaline. This potential gradient and the electrical equivalent of the pH difference (1 pH unit = 58 mV at 37°C) give a potential difference across the membrane of 100-180 mV, with the inside negative. The membrane is impermeable to protons, whose extmsion creates the potential described. 

In some cases, enzymes require the assistance of coenzymes (cofactors) to ensure the reactions proceed. Coenzymes include vitamins, metal ions, acids, and bases. They can act as transporters or electron acceptors or be involved in oxidation-reduction reactions. At the completion of the reaction, coenzymes are released, and they do not form part of the products. For some reactions that are energetically unfavorable, an energy source provided by the compound adenosine triphosphate (ATP) is needed to ensure the reactions proceed, as shown in the following reactions ... 

ATP, adenosine triphosphate A biomolecule that acts to transport energy within cells by enabling electron transfer. 

The cytochrome b(6)f complex mediates electron transfer between the PSI and PSII reaction centers by oxidizing hpophUic plastoquinol (PQH2) (see Figure 7.24) and reducing the enzymes plastocyanin or cytochrome Ce. The electronic connection also generates a transmembrane electrochemical proton gradient that can support adenosine triphosphate (ATP) synthesis instead of electron transport. 

P-Glycoprotein (P-gp), a member of the adenosine triphosphate (ATP)-binding cassette family of membrane transporters, is encoded by the human multidrug-resistance (MDRl, ABCBl) gene (15). This integral membrane protein serves as an... 

Fig. 14.1 Cellular pathway of methotrexate. ABCBl, ABCCl-4, ABC transporters ADA, adenosine deaminase ADP, adenosine diphosphate AICAR, aminoimidazole carboxamide ribonucleotide AMP, adenosine monophosphate ATIC, AICAR transformylase ATP, adenosine triphosphate SjlO-CH -THF, 5,10-methylene tetrahydrofolate 5-CHj-THF, 5-methyl tetrahydro-folate DHFR, dihydrofolate reductase dTMP, deoxythymidine monophosphate dUMP, deoxy-uridine monophosphate FAICAR, 10-formyl AICAR FH, dihydrofolate FPGS, folylpolyglutamyl synthase GGH, y-glutamyl hydrolase IMP, inosine monophosphate MTHFR, methylene tetrahydrofolate reductase MTR, methyl tetrahydrofolate reductase MTX-PG, methotrexate polyglutamate RFCl, reduced folate carrier 1 TYMS, thymidylate synthase. Italicized genes have been targets of pharmacogenetic analyses in studies published so far. (Reproduced from ref. 73 by permission of John Wiley and Sons Inc.)...

The transport is directly coupled to adenosine triphosphate (ATP) hydrolysis, which is known as primary active transport. 

Phosphorus is one of the inorganic macronutrients in all known forms of life. Inorganic phosphorus in the form of phosphate (PO/ ) plays a major role in vital biological molecules, such as DNA and RNA. Living cells also utilize phosphate to transport cellular energy via adenosine triphosphate (ATP). Phospholipids are the main structural components of all cellular membranes. Calcium phosphate salts are... 

Fujii R, Mutoh M, Sumizawa T, Chen Z, Yoshimura A, Akiyama S. Adenosine triphosphate-depen-dent transport of leukotriene C4 by membrane vesicles prepared from cisplatin-resistant human epidermoid carcinoma tumor cells. J Natl Cancer Inst 1994 86 1781-1784. 

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