Enzymes carrier systems

An immobilized enzyme-carrier complex is a special case that can employ the methodology developed for evaluation of a heterogeneous cat ytic system. The enzyme complex also has external diffusional effects, pore diffusional effects, and an effectiveness factor. When carried out in aqueous solutions, heat transfer is usually good, and it is safe to assume that isothermal conditions prevail for an immobihzed enzyme complex. 

The above conclusion is supported by the results shown in figure 4. Just as inhibitors of the 5-HT uptake carrier can antagonize MDMA-induced [ H]5-HT release in vitro, coadministration of MDMA with an uptake inhibitor such as citalopram can completely block the acute depletion of 5-HT. Although citalopram also antagonized the MDMA-induced decrease in TPH activity, there was still a significant loss of enzyme activity when compared to control. This implies that if MDMA requires access to the interior of the nerve terminals to affect TPH activity, it does not require the activity of the uptake carrier to gain entrance. Hence, these results are consistent with the outcome of synaptosomal uptake experiments with [ HJMDMA (Schmidt et al. 1987), which show that MDMA is not actively concentrated by a carrier system. Furthermore, it is apparent that the loss of enzyme activity alone is not sufficient to reduce 5-HT concentrations, but that release via the carrier must occur simultaneously, to deplete the terminal once synthetic capacity is reduced. 

There have been sustained efforts in recent years to use the carrier systems of the brush-border membrane of intestinal mucosa to increase absorption of orally administered drugs [29] [30]. One system of particular interest is the intestinal peptide carrier (hPEPTl) whose physiological function is the absorption of di- and tripeptides and whose xenobiotic substrates include /3-lactam antibiotics, renin inhibitors, and angiotensin-converting enzyme (ACE) inhibitors [31]. 

Hayashi A, Suzuki T, Shin M. An enzymic reduction system for metmyoglobin and methemoglobin, and its application to functional studies of oxygen carriers. Biochim Biophys Acta 1973 310 309. 

The Na ion concentration within the cell is maintained low, due to activity of an enzyme known as the Na+/K+ ATPase. This enzyme/carrier is present in the plasma membrane. It is an antiport system that transports three Na+ ions out of the cell and two K+ ions into the cell, for each molecule of ATP that is hydrolysed (Figure 5.10). It is responsible for maintaining a low Na+ ion concentration but a high K+ ion concentration within the ceU. Its constant activity in many it not all cells requires constant ATP hydrolysis, which accounts for more than 10% of the resting energy expenditure of an adult. 

All the internal monooxygenases that have so far been purified and characterized contain flavin coenzymes. The external hydrogen donors include reduced NAD, reduced NADP, ascorbic acid and sulfhydryl compounds. Cofactors required for the external monooxygenases are flavin, pteridine, copper, nonheme iron and heme as cytochrome P-450. In some monooxygenase reactions, enzymes and/or electron carrier systems other than monooxygenase itself are involved in the transfer of an electron or hydrogen from the external hydrogen donor to the cofactor involved. 

Iron 3-5 g 10 mg (males) 18 mg (females) Electron transport (cytochromes), oxygen carrier (haemoglobin), storage/transport (ferritin), enzymes, immune system Widespread geographically fatigue, anemia Danger in hemochromatosis, Cooley s anemia, acute poisoning, Bantu siderosis... 

The processes for the digestion and absorption of fat- and water-soluble vitamins are different, due to their solubility properties. Fat-soluble vitamins and their precursors (A, [1-carotene, D, E and K) are digested and absorbed by processes similar to those for dietary fats, mainly in the small intestine. Most water-soluble vitamins require specific enzymes for their conversion from natural forms in feed-stuffs into the forms that are ultimately absorbed. Unlike fat-soluble vitamins that are absorbed mostly by passive diffusion, absorption of water-soluble vitamins involves active carrier systems to allow absorption into the portal blood. 

Polyelectrolyte complexes can be prepared in a desired range of mass, size and structure density. The behavior of the PECs can be controlled by external parameters such as the ionic strength, the pH of the medium or the temperature. Therefore, such complexes should be of great interest as potential carrier systems for drugs, enzymes, or DNA because charged species can easily be integrated into the complex particles. 

Figure 13 shows the reaction of the double bond with Mercury (II) acetate (50). In a fast reaction the double bonds at the surface react. Subsequently controlled by a slow diffusion process, the double bonds in the interior of the particle react. The specific surface of these systems is 200 to 300 m2/g. As enzyme carriers they should be well-suited, as support for polymeric reagents more knowledge about the possibility of localizing the reaction at the surface is needed. 

Storage of norepinephrine in vesicles Dopamine is transported into synaptic vesicles by an amine transporter system that is also involved in the re-uptake of preformed norepinephrine. This carrier system is blocked by reserpine (see p. 78). Dopamine is hydroxylated to form norepinephrine by the enzyme, dopamine 3-hydroxylase. Synaptic vesicles contain dopamine or norepinephrine plus adenosine triphosphate and the 3-hydroxylase. Not all of the norepinephrine is packaged in vesicles some exists in a cytoplasmic pool that can be displaced. In the adrenal medulla, norepinephrine is methylated to yield epinephrine both are stored in chromaffin cells. On stimulation, the adrenal medulla releases about 85% epinephrine and 15% norepinephrine. 

Microgel particles have been demonstrated to be good substrates for the immobilization of enzymes, which retain their catalytic efficiency [124], However, the design of a carrier system in which the catalytic efficiency can be regulated by some extrinsic stimulation such as temperature, pH, ion intensity, or magnetism remains a challenge. Very recently, Liu et al. [125] have reported the introduction of glutathione... 

All results reviewed herein demonstrate that the microgel particles may serve as nanoreactors for the immobilization of catalytically active nanostructures, namely for metal nanoparticles and enzymes. In both cases, the resulting composites particles are stable against coagulation and can be easily handled. Moreover, the catalytic activity of metal nanoparticles can be modulated through the volume transition that takes place within the thermosensitive microgel carrier system. Similar behavior has been also observed for the temperature dependence of enzymatic activity. Thus, the microgel particles present an active carrier system for applications in catalysis. 

After the break down of proteins by proteolytic enzymes, the pancreas, and brush border peptidases, the di- and trip-eptides are absorbed through the epithelial cell membrane. Many studies have shown that intact di- and tripeptides are absorbed across the epithelial cell membrane by active transport via specific carrier systems. The absorption process is mediated by the hydrogen-coupled peptide transporter (PEPTl) located in the intestinal apical cell membrane. Because there are 20 amino acids, there may be 400... 

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