Enzymes in membranes

Highly efficient enzyme membrane reactors can be also produced by immobilizing enzymes in membranes or in hollow fibers. For example, enzymes can be confined in the porous support matrix of an asymmetric capillary membrane, while substrate-containing solution flows through the fiber lumen. The dense skin layer at the lumen wall should be impermeable to the enzyme molecules. The latter diffuse through the inner wall of the fiber to the enzyme into the spongy part, where the conversion takes place. Applied transmembrane pressure and axial flow rate are parameters that contribute to control of the reactor performance. 

Activation of Cyclic AMP Generation in Intact Cells - Forskolin activates adenylate cyclase in Intact cells and tissues with similar characteristics as those observed for activation of the enzyme in membranes and solubilized preparations. These Include preparations of rat35 and human36 adipocytes, human platelets,37 tissue slices from brain and other peripheral tissues,3° and various endocrine and secretory tissues.39 Forskolin stimulates adenylate cyclase in S49 lymphoma cells,25 32 j-at astrocytomas.rat pheochromocytoma cells, 2 cultured pituitary cells, 3-48 cardiomyocytes, >30 cultured leydlg cells,31 and cultured kidney cells.32,53 Forskolin increases intracellular cyclic AMP rapidly with an EC50 of about lOpM, and results in elevations of cyclic AMP over basal levels which range between two and fifty-fold, depending on cell type and tissue. 

A prerequisite for a role of the anion-sensitive ATPase in transport would be the localisation of the enzyme in plasma membranes, since a direct role of a mitochondrial enzyme in membrane transport can be excluded. As discussed in Section 2e, it is very likely that the anion-sensitive ATPase present in microsomal fractions of various tissues from different species is due to mitochondrial contamination. 

Brown, W. J., Chambers, K., and Doody, A. (2003). Phospholipase A2 (PLA2) enzymes in membrane trafficking Mediators of membrane shape and function. Traffic 4, 214-221. 

Another version of the urea electrode (Figure 11.17) immobilizes the enzyme in a polymer membrane formed directly on the tip of a glass pH electrode. In this case, the electrode s response is... 

In open fibers the fiber wall may be a permselective membrane, and uses include dialysis, ultrafiltration, reverse osmosis, Dorman exchange (dialysis), osmotic pumping, pervaporation, gaseous separation, and stream filtration. Alternatively, the fiber wall may act as a catalytic reactor and immobilization of catalyst and enzyme in the wall entity may occur. Loaded fibers are used as sorbents, and in ion exchange and controlled release. Special uses of hoUow fibers include tissue-culture growth, heat exchangers, and others. 

N. C. Beaton, "Advances in Enzyme and Membrane Technology," Institute of Chemical Engineers Symposium Series No. 51, Institute of Chemical Engineers, London, 1977, pp. 59—70. 

The enzyme can be immobilized on the electrode by several techniques (53). The simplest method, first used in 1962, is to trap an enzyme solution between the electrode surface and a semipermeable membrane. Another technique is to immobilize the enzyme in a polymer gel such as polyacrylamide which is coated on the electrode surface. Very thin-membrane films can be obtained by electropolymerization techniques (49,54,55) using polypyrrole, polyindole, or polyphenylenediamine films, among others. These thin films (qv) offer the advantage of improved diffusion of substrate and product that... 

Erythrocyte Entrapment of Enzymes. Erythrocytes have been used as carriers for therapeutic enzymes in the treatment of inborn errors (249). Exogenous enzymes encapsulated in erythrocytes may be useful both for dehvery of a given enzyme to the site of its intended function and for the degradation of pathologically elevated, diffusible substances in the plasma. In the use of this approach, it is important to determine that the enzyme is completely internalized without adsorption to the erythrocyte membrane. Since exposed protein on the erythrocyte surface may ehcit an immune response following repeated sensitization with enzyme loaded erythrocytes, an immunologic assessment of each potential system in animal models is required prior to human trials (250). 

Cell membrane The cell membrane is composed of about 45% lipid and 55% protein. The lipids form a bilayer that is a continuous nonpolar hydrophobic phase in which the proteins are embedded. The cell membrane is a highly selective permeability barrier that controls the entry of most substances into the cell. Important enzymes in the generation of cellular energy are located in the membrane. 

The inhibition analyses were examined differently for free lipase in a batch and immobilised lipase in membrane reactor system. Figure 5.14 shows the kinetics plot for substrate inhibition of the free lipase in the batch system, where [5] is the concentration of (S)-ibuprofen ester in isooctane, and v0 is the initial reaction rate for (S)-ester conversion. The data for immobilised lipase are shown in Figure 5.15 that is, the kinetics plot for substrate inhibition for immobilised lipase in the EMR system. The Hanes-Woolf plots in both systems show similar trends for substrate inhibition. The graphical presentation of rate curves for immobilised lipase shows higher values compared with free enzymes. The value for the... 

Some of the critical enzymes in our cells are metalloproteins, large organic molecules made up of folded polymerized chains of amino acids that also include at least one metal atom. These metalloproteins are intensely studied by biochemists, because they control life and protect against disease. They have also been used to trace evolutionary paths. The d-block metals catalyze redox reactions, form components of membrane, muscle, skin, and bone, catalyze acid-base reactions, control the flow of energy and oxygen, and carry out nitrogen fixation. 

Hypothermia slows down enzyme catalysis of enzymes in plasma membranes or organelle membranes, as well as enzymes floating around in the cytosol. The primary reason enzyme activity is decreased is related to the decrease in molecular motion by lowering the temperature as expressed in the Arrhenius relationship (k = where k is the rate constant of the reaction, Ea the activation energy,... 

Tyler DD, Sutton CM Respiratory enzyme systems in mitochondrial membranes. In Membrane Structure and Function, vol 5. Bittar EE (editor). Wiley, 1984. 

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