Enzyme immobilisation advantages

Another case of heterogeneous systems refers to immobilized enzymes. The kinetic behaviour of a bound enzyme can differ significantly from that of the same enzyme in free solution. The properties of an enzyme can be modified by suitable choice of the immobilisation protocol, whereas the same method may have appreciably different effects on different enzymes. These changes may be due to conformational alterations within the enzyme, immobilisation procedure, the presence and nature of the immobilisation support. The advantages of immobilised enzymes are for instance in reusability and possibility to use continuous mode. 

The use of immobilised cells for industrial and analytical enzymic processes is prophetically advantageous, the problems of isolation of the enzyme(s) and separation of the enzyme(s) from the product being avoided. However, the majority of the reaction currently used for direct enzyme immobilisation would cause cell death if applied to cells. Our approach has been based on the ability of water-insoluble metal hydroxides to chelate and retain peptides, proteins, etc. including enzymes. From various studies it was concluded that gelatinous titanium and zirconium hydroxide matrices are effective matrices for enzyme etc. immobilisation. Their advantages include low cost, convenient preparation (which may be conducted in any location without specialised facilities), the absence of any need for pre-preparation, ability to couple enzyme at neutral pH, the high retentions of specific activity of the enzyme on immobilisation, and the ability of modification to exert microenvironmental effects on and thereby alter the characteristics of the immobilised enzyme. 

The work-up of batch processes, run in stirred vessels, had often faced the challenge to efficiently separate and recover the enzyme used. Meanwhile, there is abundant know-how available to immobilise enzymes on different carriers, though some issues need always to be considered maintained activity of the enzyme, its stability towards solvents and the operating temperature used in a reaction. Enzyme immobilisation allows for continuous reactions carried out in columns or in a sequence of continuous stirred-tank reactors. Certain advantages are offered by Degussa s enzyme-membrane-reactor (EMR), where the enzyme is surrounded by a hoUow-fibre membrane, that is permeable to substrate and product. 

Potentiometry is a rarely used detection method employed in biosensors, with enzymes immobilised in an electrodeposited polymer layer, although certain advantages over... 

The introduction of immobilised enzymes has several advantages over the chemical de-acylation of fl-lactam. List as many as you can. (You may need to refer back to Figures 6.13-6.16 and the associated text... 

Polysaccharides can also be used to immobilise cells or enzymes, permitting the re-use of the catalyst and continuous flow systems. Alginates have the advantage that gel formation occurs under mild conditions, therefore cells remain viable and enzymes are not denatured but calcium gradually leaches out and the gel dissolves. Gellan or other combinations may prove superior for this application. 

Several L-amino acids are produced on a large scale by enzymatic resolution of N-acetyl-D,L-amino adds (Figure A8.4). Acylase immobilised on DEAE-Sephadex is for example employed in a continuous process while Degussa uses the free acylase retained in a membrane reactor. In the latter process the advantage of reuse of the enzyme and homogeneous catalysis are combined. 

Almost all types of cell can be used to convert an added compound into another compound, involving many forms of enzymatic reaction including dehydration, oxidation, hydroxyla-tion, animation, isomerisation, etc. These types of conversion have advantages over chemical processes in that the reaction can be very specific, and produced at moderate temperatures. Examples of transformations using enzymes include the production of steroids, conversion of antibiotics and prostaglandins. Industrial transformation requires the production of large quantities of enzyme, but the half-life of enzymes can be improved by immobilisation and extraction simplified by the use of whole cells. 

Since 1978, several papers have examined the potential of using immobilised cells in fuel production. Microbial cells are used advantageously for industrial purposes, such as Escherichia coli for the continuous production of L-aspartic acid from ammonium fur-marate.5,6 Enzymes from microorganisms are classified as extracellular and intracellular. If whole microbial cells can be immobilised directly, procedures for extraction and purification can be omitted and the loss of intracellular enzyme activity can be kept to a minimum. Whole cells are used as a solid catalyst when they are immobilised onto a solid support. 

Immobilised cells have all the advantages of immobilised enzymes. Cell immobilisation is preferred for reactions catalysed by intracellular enzymes because it avoids tedious and expensive extraction and purification procedures, which often result in preparations of low yield and stab ty. 

Among the suitable organic solvents for cyanohydrin synthesis, diisopropyl ether is especially advantageous, since when using it the enzyme activity remains almost constant over a long period of time [139]. In the case of ethyl acetate as reaction medium, a more or less rapid inactivation of the oxynitrilase was observed. However, it seemed to be necessary to immobilise the enzyme to enhance its stability [140], which can be advantageous with respect to reisolation and reusage of the enzyme preparation [2]. 

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