How does temperature and pH effect the function of enzyme?

Answer 1

Raising the temperature will denature an enzyme so that it is no longer functional. Lowering the temperature will reduce the rate of the reaction so low as to make it seem non-functional. Altering the pH above or below its optimum pH will also reduce the enzyme's activity, and at extremes the enzyme may be permanently denatured. Here's why:

* Proteins fold into particular shapes that are vital for (and determine) their function. * The shape a protein will fold into is determined by its amino acid sequence, since different amino acids have different properties. * Each amino acid has a 'side chain' sticking out of the main polypeptide chain, which will have specific chemical properties capable of forming certain interactions with other amino acids in the protein (as well as with water and other molecules).

* It is these intramolecular forces (interactions between different amino acids within a protein) that are responsible for producing and maintaining the shape of the protein. The forces are:

* Hydrogen bonds - weak bonds between slightly positively charged hydrogen and slightly negatively charged atoms (such as oxygen). * Electrostatic interactions - weak attractive forces between charged regions of the protein, including only small charges resulting from polar bonds. * Disulphide bridges * Hydrophobic interactions

* Hydrophobic interactions are not sufficient to hold a protein in a particular shape, only to pull the protein into a ball to help it fold into the correct shape. * Hydrogen bonds and electrostatic interactions are dependent on interactions between charges. pH is a measure of the concentration of hydrogen ions, which are positively charged. If there were more hydrogen ions in the solution than the protein was designed for, these ions would compete for the interactions holding the protein together, as well as protonating groups that need to be deprotonated to form important intramolecular interactions (eg nitrogen). Equally, if there were too few hydrogen ions in the solution, the same interactions would disrupted by the relatively high concentration of hydroxide (OH) ions, and important protonated groups may become deprotonated.* Increasing the temperature increases the energy of the bonds and atoms in the protein, to the point at which there is enough energy to overcome the force of the intramolecular reactions, resulting in them breaking.

* Disruption of the interactions in any case will lead to some of the protein losing its ability to be held in a certain shape, which then reduces it's catalytic activity (as catalytic activity relies on the shape). The loss of activity will be proportional to the extent of the disruptions, which will in turn be proportional to the extent of the change in pH or temperature. * Disulphide bonds would also be reduced (broken) at very low pH, and broken at extremely high temperatures (though other interactions will have already broken and destroyed activity before this temperature/pH is reached). * Therefore, all proteins have a pH and temperature at which they have been designed to work that they will work very well at. The further away from the pH the solution gets, the more of the proteins will be effected by the change, until eventually they are all completely denatured. This concept is similar to the collision theory, in that a small change in pH will reduce activity, but not significantly, because very few of the increased hydrogen/hydroxide ions will actually be competing for the intramolecular interactions at any one time. Typically, a protein will work best at about 40oC and pH 7. The activity approximately halves with every 10oC drop in temperature between 0 and 40. The activity with varying pH resembles a normal distribution curve.

Answer 2

Every enzyme has an optimum temperature and pH, at which it has the best or "optimum"activity. So any change in temperature and pH will lead to inactivation of the enzyme. Since most enzymes are protein in nature, temperatures higher than the optimum for the particular enzyme (every enzyme has its own unique and specific optimum pH and temperature) can lead to denaturation of the proteinaceous enzyme. Similarly, too much of a change in pH (higher or lower) can lead to damage of the enzyme.