Epnzymatric recycling of coenzymes by a multi-enzyme system immobilized within semipermeable collodion microcapsules

Colorimetric method for enzymatic screening assay of ATP using Fe(III)-xylenol orange complex formation

In hygiene management, recently there has been a significant need for screening methods for microbial contamination by visual observation or with commonly used colorimetric apparatus. The amount of adenosine triphosphate (ATP) can serve as the index of a microorganism. This paper describes the development of a colorimetric method for the assay of ATP, using enzymatic cycling and Fe(III)-xylenol orange (XO) complex formation. The color characteristics of the Fe(III)-XO complexes, which show a distinct color change from yellow to purple, assist the visual observation in screening work. In this method, a trace amount of ATP was converted to pyruvate, which was further amplified exponentially with coupled enzymatic reactions. Eventually, pyruvate was converted to the Fe(III)-XO complexes through pyruvate oxidase reaction and Fe(II) oxidation. As the assay result, yellow or purple color was observed: A yellow color indicates that the ATP concentration is lower than the criterion of the test, and a purple color indicates that the ATP concentration is higher than the criterion. The method was applied to the assay of ATP extracted from Escherichia coli cells added to cow milk.

Artificial cells with emphasis on bioencapsulation in biotechnology

The most common use of artificial cells is for bioencapsulation of biologically active materials. Each artificial cell can contain combinations of materials. The permeability, composition and shape of an artificial cell membrane can be varied using different types of synthetic or biological materials. These possible variations in contents and membranes allow for large variations in the properties and functions of artificial cells. Artificial cells containing adsorbents have been a routine form of treatment in hemoperfusion for patients. This includes acute poisoning, high blood aluminum and iron, and supplement to dialysis in kidney failure. Artificial red blood cell substitutes based on modified hemoglobin are already in Phase I and Phase II clinical trials in patients. Artificial cell encapsulated cell cultures are being studied for the treatment of diabetes, liver failure, gene therapy and other conditions. Research on artificial cells containing enzymes includes their use for treatment in hereditary enzyme deficiency diseases and other diseases. Recent demonstration of extensive enterorecirculation of amino acids in the intestine has allowed oral administration to deplete specific amino acids. One example is phenylketonuria, an inborn error or metabolism resulting in high systemic phenylalanine levels. Preliminary clinical studies in patients using bioencapsulation of cells or enzymes have started. Artificial cells containing complex enzyme systems convert wastes like urea and ammonia into essential amino acids. Artificial cells are being used for the production of monoclonal antibodies, interferon and other biotechnological products. Other areas of biotechnological uses include drug delivery, and other areas of biotechnology, chemical engineering and medicine.

Artificial cells in immobilization biotechnology

Artificial cells contain biologically active materials. Artificial cells containing adsorbents have been a routine form of treatment in hemoperfusion for patients. This includes acute poisoning, high blood aluminum and iron, and supplement to dialysis in kidney failure. Artificial cells are being tested for use as red blood cell substitutes. Artificial cells encapsulated cell culture are being tested in animals for the treatment of diabetes and liver failure. A novel 2 step method has prevented xenograft rejection. Artificial cells containing enzymes are being studied for treatment in hereditary enzyme deficiency diseases and other diseases. Recent demonstration of extensive enterorecirculation of amino acids in the intestine has allowed its oral administration to deplete specific amino acids. Artificial cells containing complex enzyme system convert wastes like urea and ammonia into essential amino acids. Artificial cell is being used for the production of monoclonal antibodies, interferons and other biotechnological products. It is also being investigated for drug delivery, and for use in other applications in biotechnology, chemical engineering and medicine.

Recycling of NAD(P) by multienzyme systems immobilized by microencapsulation in artificial cells

Multistep enzyme systems can be immobilized in solution within semipermeable microcapsules. With the ability to recycle cofactors, a number of potentially useful systems have been made possible. Furthermore NAD+ can be retained inside the microcapsules by two approaches. (1) NAD+ can be linked to macromolecules such as dextran or polyethyleneimine. However, in this form, there are significant increases in steric hindrance and diffusion restrictions. (2) "Artificial cells" consisting of lipid-polyamide membrane microcapsules containing multienzyme systems, cofactors, and substrates can retain NAD+ in the free form. Analogous to the intracellular environments of red blood cells, free NAD+ in solution inside the microcapsules is effectively recycled by the multistep enzyme systems which are also in solution. Enzymes in the microcapsules are in high concentrations and in close proximity to one another. Any number and any concentration of different enzyme systems can be microencapsulated all within one artificial cell, within the limit of solubility of the total amount of enzymes. Products of sequential reactions inside the microcapsules are at much higher concentrations than outside. All these factors result in an optimal intracellular environment for multistep enzyme reactions. External substrates in the form of lipophilic or small hydrophilic molecules can equilibrate across the membrane to participate as initial substrates in the multistep reactions in the microcapsules. A number of potential applications are possible using this approach. The lipid-polyamide membrane artificial cell can also be used in basic research as a biochemical cell model for the simpler types of biological cells such as erythrocytes.

Artificial cells in medicine and biotechnology

Since the feasibility of artificial cells was first demonstrated in 1957 [Chang (1, 2)], an increasing number of approaches to their preparation and use have become available. Thus artificial cell membranes can now be formed using a variety of synthetic or biological materials to produce desired variations in their permeability, surface properties, and blood compatibility. Almost any material can be included within artificial cells. These include enzyme systems, cell extracts, biological cells, magnetic materials, isotopes, antigens, antibodies, vaccines, hormones, adsorbents, and others. Since cells are the fundamental units of living organisms, it is not surprising that artificial cells can have a number of possible applications. This is especially so since artificial cells can be "tailor-made" to have very specialized functions. A number of potential applications suggested earlier have now reached a developmental stage appropriate for clinical trial or application. These clinical applications include the use of such cells as a red blood cell substitute, in hemoperfusion, in an artificial kidney or artificial liver, as detoxifiers, in an artificial pancreas, and so on. Artificial red blood cells based on lipid-coated fluorocarbon or crosslinked hemoglobin are being investigated in a number of centers. The principle of the artificial cells is also being used in biotechnology to immobilize enzymes and cells. Developments in biotechnology have also resulted in the use of the principle underlying the artificial cell to help produce interferons and monoclonal antibodies; to create immunosorbents; to develop an artificial pancreas; and to bring enzyme technology usefully into biotechnology and biomedical applications. Artificial cells are also being used as drug delivery systems based on slow release, on magnetic target delivery, on biodegradability, on liposomes, or other approaches. The present status and recent advances will be emphasized in this paper.

Effects of glucose dehydrogenase in converting urea and ammonia into amino acid using artificial cells

A microencapsulated multienzyme system containing urease, glutamate dehydrogenase and glucose dehydrogenase has been used to convert urea and ammonia into an amino acid. The effect of two different glucose dehydrogenases was studied in detail. High-specific-activity glucose dehydrogenase requires minimal cofactor and glucose and can greatly facilitate the further development of this approach for possible clinical applications.

NAD recycling in the collagen membrane

NAD recycling in the collagen membrane was investigated as follows: (1) Alcohol dehydrogenase and lactate dehydrogenase were co-immobilized in the collagen membrane and the rate of lactate production by immobilized enzymes was compared with that of free enzymes by using free NAD. An increased rate was observed in the case of immobilized enzyme. (2) The soluble high molecular weight derivatives of NAD (dextran-NAD) were immobilized in the collagen membrane with the two dehydrogenases and recycling of dextran-NAD in the membrane was examined. Lactate was produced by the membrane without adding free NAD. The interaction between the high molecular weight NAD derivatives and enzymes are also discussed.