Multienzyme Systems (bi- and Polyfunctional Enzymes) by Gene Fusion
Multienzyme systems have been artificially synthesized, which can catalyze sequential reactions in many biotechnological production processes. Although, proximity of more than one enzymes can also be achieved by co-immobilization and chemicacrossl -linking, gene fusion appears to have the highest potential in enzyme technology.

During 1990-2000, a variety of artificial bifunctional and polyfunctional enzymes were prepared by gene fusion in vitro, and their physical and chemical properties anaylsed. Some of them include the following: β-Galactosidase-galactokinase. Sequential hydrolysis of lactose to glucose is achieved by β- galactosidase (dimeric) and galactokinase (dimeric) enzyme. The product of the fused genes (both genes from E. coli) was found to be a tetramer, each polypeptide carrying an active site for each of the two enzymes.

β-Galactosidase-galactose dehydrogenase ­galactokinase. A trifuctional enzyme carrying all the three activities on the same polypeptide was prepared using a chimaeric fused gene, cloned in vector pDZKI0. The enzyme was a tetramer or an octamer.
Galactose dyhydrogenase - luciferase. Bacterial luciferase is a heterodimer with two subunits (α and β encoded by luxA and luxB). Only IuxB was fused with the gene for galactose dehydrogenase. The bifunctional enzyme generated much higher bioluminiscent peaks compared with a mixture of native component enzymes.
Advantages of multienzymes. Following are some of the additional advantages of multienzymes : (i) Their purification is simplified. (ii) These are useful in connection with biosensors, (iii) They are also useful in the development of metabolic engineering. It is, therefore, believed that the preparation of such artificial multienzyme systems, will be most valuable in the construction of microorganisms by inserting these fused genes through transformation.