Discuss the lock-and-key theory of enzyme-substrate interaction giving a specific example to illustrate the theory

Discuss the lock-and-key theory of enzyme-substrate interaction giving a specific example to illustrate the theory. Include in your discussion the effects of each of the following: substrate concentration, pH shifts, temperature shifts, and competitive inhibition.

In the late 1800s and very early 1900s, Emil Fischer proposed the analogy of enzyme reactions with that of keys and locks. The lock-and-key theory of enzyme-substrate interaction consists of the two components: the enzyme that catalyzes the reaction, and the substrate that is catalyzed by the enzyme. The substrate binds to the enzyme at the point known as the active site and this bindings causes the electrons in the substrate to be rearranged and ultimately released for the enzyme catalyzing process can take place again.

Fischer's particular analogy relates enzymes as the locks and the substrates as the key. Only specific keys can turn the lock just as only specific substrates can cause an enzyme to react. The wrong key and the wrong substrate will not turn the lock or cause the enzyme to react. Some enzymes only transport materials in and out of the cell (think integral proteins) and these serve as an excellent example where peripheral proteins (the exposed proteins on the surface of the plasma membrane) grab materials that are surrounding the cell and then pull them inwards through the width of the integral protein and then back into the cell. Only specific materials (substrates) actually “fit” into the active site on the peripheral proteins.

An increase in substrate concentration will decrease the rate at which the entirety of the solution has been catalyzed by some specific enzyme. Increasing the percent of enzymes in the solution would increase the overall rate of catalysis and lead to the absence of further substrates to catalyze more quickly than when there is, say, one thousand parts substrate for every one part enzyme.

Changing the acidity of the solution means you are either adding or removing hydrogen ions. These hydrogen ions are not at all neutral. These free-floating hydrogen ions (such as hydronium) actually interact with their environment and usually inhibit enzyme catalysis. In all cases, increasing or decreasing the average kinetic energy of the solution (change of temperature) at some point causes the enzymes to unfold and unravel all the way back to their primary level and then some. Not all enzymes will decay at precisely the same rate and the results will not likely ever be the same from experiments since temperature is only the measure of the average kinetic energy and not the kinetic energy at some specific site (i.e., each individual enzyme molecule).

Enzymes are not “perfect locks” and like all locks they at least allow each key (substrate) a chance to try it all out. Inhibitors bind to the active site of the enzyme but do not necessarily trigger the reaction that is expected and instead the key sits there. In this situation the inhibitor is taking up valuable active sites that could be used to catalyze substrate reactions that are then blocked due to the presence of the inhibitor in the `key hole' (active site).