Two samples of anenzyme are heated to 60oC and

90oC, respectively for 5 minutes,

and then allowed tocool. Discuss the effects of

this on the function and structureof

the enzyme.

b) An enzyme isolatedfrom the thermophilic

bacterium Thermophilus aquaticus is

capable ofwithstanding prolonged incubation at

70oC, and still retain activity. What

properties of the protein mightcontribute to this stability?

Answer and Explanation:

a) As a protein solution is heated, intramolecular bonds in its tertiary and quaternary structure are broken, so the protein is unfolded and loses its conformation. This process is called denaturation (loss of native conformation) and affects to the active sites if the protein is an enzyme, so the function can be also affected. The sample heated at 60ºC can suffer reversible denaturation because it is a low temperature, but it depends of the protein and its denaturation temperature. Reversible process are unfolding process that can be reverted upon sample cooling. The sample heated at 90ºC will probably suffer irreversible denaturation and a total loss of its functionality due to the high temperature.

b) Enzymes from thermophilic organisms are capable of retain their conformation upon heating at high temperatures (above 50ºC), because the organisms they came from are adapted to the living at high temperatures. The structure of these proteins have certain properties which contribute to its thermostability: the presence of extra hydrogen bonding and disulphide bridges, compactness of protein structure, oligomerization and a higher strenght interaction between subunits. These features avoid the fast disruption of the intramolecular bonding by thermal energy.