Hydrogen ions active pumping

Almost all cells have an active transport system to maintain nonequilibrium concentration levels of substrates. For example, in the mitochondrion, hydrogen ions are pumped into the intermembrane space of the organelle as part of producing ATP. Active transport concentrates ions, minerals, and nutrients inside the cell that are in low concentration... 

Mechanism of Action Aproton pump inhibitor that is converted to active metabolites that irreversibly bind to and inhibit hydrogen-potassium adenosine triphosphates, an enzyme on the surface of gastricparietal cells. Inhibits hydrogen ion transport into gastric lumen. Therapeutic Effect Increases gastricpH, reducing gastric acid production. 

Other active transport systems include the sodium-hydrogen ion pump of the Gl tract (stomach) and the calcium ion pump which helps to maintain a low concentration of calcium in the cytosol. 

Oxidative phosphorylation occurs in the mitochondria of all animal and plant tissues, and is a coupled process between the oxidation of substrates and production of ATP. As the TCA cycle runs, hydrogen ions (or electrons) are carried by the two carrier molecules NAD or FAD to the electron transport pumps. Energy released by the electron transfer processes pumps the protons to the intermembrane region, where they accumulate in a high enough concentration to phosphorylate the ADP to ATP. The overall process is called oxidative phosphorylation. The cristae have the major coupling factors F, (a hydrophilic protein) and F0 (a hydrophobic lipoprotein complex). F, and F0 together comprise the ATPase (also called ATP synthase) complex activated by Mg2+. F0 forms a proton translocation pathway and Fj... 

Electrons in the iron-sulfur clusters of NADH-Q oxidoreduetase are shuttled to coenzyme Q. The flow of two electrons from NADH to coenzyme Q through NADH-Q oxidoreduetase leads to the pumping offour hydrogen ions out of the matrix of the mitochondrion. The details of this process remain the subject of active investigation. However, the coupled electron- proton transfer reactions of Q are crucial. NADH binds to a site on the vertical arm and transfers its electrons to FMN. These electrons flow within the vertical unit to three 4Fe-4S centers and then to a bound Q. The reduction of Q to... 

Cimetidine (Tagamet) and other H2-receptor antagonists (such as ranitidine [Zantac] and famotidine [Pepcid]) block botli the morphological transformation of the parietal cell and secretion. Proton pump inhibitors (PPIs) have a different mechanism of action. Omeprazole (a PPI) is taken up by the parietal cell and converted to an active metaboHte that inactivates the parietal H", IC-ATPase. Hydrogen ion secretion is inhibited until new ATPase is synthesized—a process that requires at least 24 hours. 

Diagrammatic representation of the production of stomach acid. Carbon dioxide from metabolic processes is converted to carbonic acid under the influence of carbonic anhydrase. Carbonic acid and sodium chloride dissociate, hydrogen ion is actively pumped across the parietal cell membrane and associates with free chloride ion. The remaining sodium and bicarbonate ions combine and remain in the plasma to be utilized in the acid-base buffering system. 

Proton pump inhibitors may affect renal, and possibly hepatic, clearance of methotrexate by inhibition of methotrexate transporter proteins. It has been suggested that omeprazole may inhibit the activity of a hydrogen-ion dependent mechanism in the kidney, on which methotrexate depends for its excretion, so that its loss is diminished. It has also been suggested that the situation with lansoprazole may be similar, but that pantoprazole may differ since at about the pH found in the renal tubules (pH 5), pantoprazole is more slowly activated than omeprazole. However, a case of an interaction with pantoprazole has also been reported. ... 

The main cause of death of species in acid lakes is the excessive loss of sodium ions, which cannot be rapidly replaced by active transport. The disruption of sodium/potassium pump mechanism has been attribute to the presence of high concentrations of hydrogen ions. 

If tubular reabsorption does not meet physiological requirements, a renal tubular mechanism for generating bicarbonate is called into play this mechanism is shown in outline in Figure 1.4B. Carbon dioxide from metabolism reacts with water to yield hydrogen ions, which are actively pumped into the tubular fluid rendering the urine acid, and bicarbonate ions, which diffuse into the renal interstitial fluid and hence into the general extracellular fluid of the body. The tubules continually add bicarbonate to the body by this mechanism. 

In recent years, there have been several successful attempts to use lasers for re-exciting ions after they have been cooled down. Since the ion cloud consists of a limited number, various strategies are possible for deriving information on state specific collision dynamics. The methods range from a dedicated perturbation of a stationary low temperature equilibrium via burning a hole into the state population to two colour pump — probe experiments. Most of such activities are used for spectroscopy or for understanding the low temperature populations of trapped hydrogen ions. They are discussed in Chapter 6. 

Hydrogen ions are often needed in biochemical reactions carried out by enzymes. Several such enzymes use water wires to shuttle the ions from the solvent through the protein and into the active site where the reaction takes place. This happens, for example, in cytochrome and peroxidase enzymes, and in bacterio-rhodopsin, a light-driven proton pump used by some Archaea to transport protons across a membrane during the conversion of light energy into chemical energy. 

It can be predicted [114-115] that a pumping effect similar to the preceding one can be produced with the two sequential enzymes mixed together in one layer if their respective activities are different functions of substrate concentration or, more generally, if one of them is inhibited (or not activated) in the first part of the membrane and the other one in the other part. For the sake of simplicity, this can be illustrated with a hydrogen ion gradient and two enzymes of different optimal pH, When the hydrogen... 

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