The interaction of an enzyme with its substrate.
Note: the lock and key model once in favor has been abandoned since it did not describe how the substrates bonds could be broken.
The ability of an enzyme to catalyze a reaction depends on its three-dimensional shape. The shape of the protein in turn depends on a variety of environmental factors including temperature and pH.
Enzymes have an optimal temperature. The rate of an enzyme-catalyzed reaction increases with rising temperature up to the point at which thermal vibrations break the hydrogen, hydrophobic and even the ionic bonds critical in maintaining its tertiary or quaternary structures. Temperatures within the acceptable range can double the rate of a reaction for every 10 degrees of increase.
pH can denature (not necessarily destroy) an enzyme by disrupting the hydrogen bonding within the molecule. Enzymes have an optimum pH which can be seen in the activity curves below.
Many enzymes require another molecule other than the substrate to be fully active. These may be cofactors or coenzymes
Inhibitors. Enzyme inhibitors selectively prevent enzymatic action by combining:
Inhibitors can be classified as competitive or noncompetive
Enzymes can also be activated (and regulated) at an allosteric site which is generally part of the quatenary structure of the protein. This site explains the process of allosteric activation.
An enzyme that is involved in a catabolic pathway such as respiration can be inhibited by the production of ATP and activated by an increase in ADP. The temporary attachment of these metabolites at the allosteric site of the enzyme strongly depends upon their concentrations. The competition between ATP (inhibition) and ADP (activation) for the allosteric site is a classic example of homeostasis.
Modified July 10, 2005