ABSTRACT
The rates of enzyme-catalyzed reactions in biological systems are altered by activators and inhibitors, collectively known as effector molecules. In biological systems the rates of many enzymes are altered by the presence of other molecules such as activators and inhibitors. A common theme in the control of metabolic pathways is when an enzyme early on in the pathway is inhibited by an end-product of the metabolic pathway in which it is involved. A phosphorylated enzyme may be either more or less active than its dephosphorylated form. Thus phosphorylation/dephosphorylation may be used as a rapid, reversible switch to turn a metabolic pathway on or off according to the needs of the cell. The digestive enzymes trypsin, chymotrypsin and elastase are produced as zymogens in the pancreas. Factors affecting the rate of synthesis include the level of induction or repression of the gene encoding the enzyme and also the rate of degradation of the mRNA produced from that gene.
