In E. coli,
synthesis of β galactosidase,
an enzyme meant for hydrolysis of lactose into glucose and galactose, has been studied in considerable detail.
If βgalactosides (e.g. lactose) are not supplied to E. coli
cells, the presence of β galactosidase is hardly detectable, but as soon as lactose is added, production of enzyme β galactosidase increases (Fig. 35.1) as much as 10,000 times. The enzyme quantity again falls down as quickly as the substance (i.e. lactose) is removed. Such enzymes, whose synthesis can be induced by adding the substrate are known as inducible
enzymes and the genetic systems responsible for the synthesis of such an enzyme are known as inducible