Regulation of enzyme synthesis and breakdown

The amount of a specific enzyme present in a tissue or cell modifies according to the rates of its degradation and synthesis.

Factors affecting the rate of synthesis involve the level of induction or repression of the gene encoding the enzyme and also the rate of degradation of the mRNA produced from in which gene. Several key enzymes at control points in metabolic pathways have particularly short-lived mRNAs and the rate of enzyme synthesis is therefore readily controlled through factors which affect the rate of gene transcription.
The rate of degradation of an enzyme is reflected in its half-life – the time taken for 50 percent of the protein to be degraded. Most enzymes which are important in metabolic regulation have short half-lives and are termed labile enzymes.