Enzymes leakage

The adsorption should be strong enough to insure no enzyme leakage under process operation. In the eharaeterization of a carrier material, adsorption isotherms of enzyme adsorbed to the earrier ean illustrate the enzymes affinity towards the carrier material and the maximum amount of enzyme, whieh ean be adsorbed on the material (Rexova-Benkova, 1992 and Gitlesen, Bauer Adlerereutz, 1997). 

The liver is involved in a variety of both synthetic and catabolic functions, including metabolism of amino acids, lipids, carbohydrates, protein synthesis and detoxification [ 1 ]. These metabolic functions are performed mainly by hepatocytes, although the liver is made of three major cell types (hepatocytes, biliary epithelial cells and Kupffer cells). Exerting many different metabolic functions, the liver contains several different and specific enzymes, leakage of which into the bloodstream occurs in hepatic diseases. 

In in vitro systems, criteria of toxicity will generally be measurements of either specific biochemical changes, such as ATP level or protein synthesis, or general indicators such as cell metabolic activity, viability, or membrane damage as indicated by dye uptake or enzyme leakage. 

Although the main advantage of this class of reactors is the retention and reuse of the enzyme, some effects usually cause a decrease of enzymatic activity [110] (1) enzyme leakage through the membrane (2) adsorption of the enzyme onto the membrane, which causes alterations in enzyme conformation (3) interactions with the membrane material, which may influence the stability of the enzyme (4) shear forces and friction near the membrane [98] and (5) peroxide deactivation. 

Two main criteria for the membrane selection are pore size and material. As peroxidases usually have sizes in the range of 10-80 kDa, ultrafiltration membranes with a molecular cutoff between 1 and 50 kDa are the most adequate to prevent enzyme leakage [99]. The materials commonly applied to ultrafiltration membranes are synthetic polymers (nylon, polypropylene, polyamide, polysulfone, cellulose and ceramic materials [101]. The adequate material depends on a great number of variables. When enzyme is immobilized into the matrix, this must be prepared at mild conditions to preserve the enzymatic activity. In the case of enzyme immobilization onto the membrane, this should be activated with the reactive groups necessary to interact with the functional groups of the enzyme. If an extractive system is considered, the selection of the hydrophilicity or hydro-phobicity of the membrane should be performed according to the features of reactants, products, and solvents. In any case, the membrane should not interfere with the catalytic integrity of the enzyme. 

Hannemann Jand Baumann K. Inhibition of lactate-dehydrogenase by cisplatin and other platinum-compounds enzyme leakage of LDH is not a suitable method to measure platinum-compound-induced kidney cell damage nv/fro. ResCommun Chem Pathol Pharmacol 60 371 -379,1988. 

The system has been improved through redesigning the closed-flow microdialysis perfusion system of the sensor to minimize the risk of enzyme leakage by immobilizing the enzymes GOD and catalase in an enzyme reactor. 

Skeletal muscles also contribute enzymes to blood. Again, the cause may be poor perfusion, hypotliermia, or direct trauma to the muscles (crush injuries). Infection, inflammation (polymyositis), degenerative changes (dystrophies), drugs, and alcohol (alcoholic myopathy) wid cause enzyme leakage from myocytes. Enzyme release from muscles and other tissues also occurs as a result of anesthesia. 

Lee outlines three different physical methods that are commonly utilized for enzyme immobilization. Enzymes can be adsorbed physically onto a surface-active adsorbent, and adsorption is the simplest and easiest method. They can also be entrapped within a cross-linked polymer matrix. Even though the enzyme is not chemically modified during such entrapment, the enzyme can become deactivated during gel formation and enzyme leakage can be problematic. The microencapsulation technique immobilizes the enzyme within semipermeable membrane microcapsules by interfacial polymerization. All of these methods for immobilization facilitate the reuse of high-value enzymes, but they can also introduce external and internal mass-transfer resistances that must be accounted for in design and economic considerations. 

The immobilization of enzymes onto CNTs leads in most cases in the stabilization of the immobilized enzyme [108, 135], The stability was further enhanced when covalent bond between the enzyme and the nanomaterials were used [13, 119, 137]. The covalent bond prevents the enzyme leakage during repeating used of the enzyme-nanomaterial conjugates. When the enzymes are non-covalently attached onto the nanomaterials, the enzyme molecules are in equilibrium between the solid state (the microenvironment of the nanomaterial) and the bulk liquid phase, so that in every use some molecules are detached from the nanomaterial. 

Enzyme leakage, tion and abrasion in and enzyme loading... 

Usuda, K., K. Kono, T. Dote, H. Nisbiura, and T. Tagawa. 1999. Usefnlness of the assessment of urinary enzyme leakage in monitoring acnte flnoride nephrotoxicity. Archives of Toxicology 73 346-351. 

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