An enzymes main purpose in our cells is to speed up reaction rates by lowering the activation energy at the transition state. The reason that enzymes interact with the substrate the most at the transition state rather then with the reactants is due to the amount of interactions it would need to break in order to proceed with the reaction. With the most interactions taking place in the beginning of the process there would be no incentive for the reaction to proceed seeing as though the enzyme and substrate are happily bound together. Due to the fact that substrates and enzymes are always moving, the enzyme will bind with the substrate and limit its ability to change shape forcing it to change conformation into the transition state of the reaction, this is when optimal interactions will take place.
There are two main types of enzymes, Michaelis Menten and allosteric, each demonstrating key differences between enzymes and their abilities. Michaelis Menten is a kind of enzyme that demonstrates a hyperbolic curve whereas allosteric enzymes portray a sigmoidal curve due to their feature of having multiple subunits. The subunits of allosteric enzymes can be in two forms, either T form or R form, meaning they are less active or more active respectively. Positive cooperativity takes place between subunits of an allosteric enzyme when switching from the T form to the R form. This means that when one substrate binds to a subunit in the T form is causes the substrate to change conformation therefore causing a conformational shift in the neighboring subunits resulting in more R form. With more R form of the enzyme, the affinity is increased allowing the substrate to be more likely to bind to the enzyme.
One main way to regulate enzyme function in a cell is through the production of inhibitors. Inhibitors can get very tricky due to the fact that there are many different kinds of them. Not only are there irreversible and reversible kinds, but there are also competitive, uncompetitive and mixed. These all depend on where the inhibitor binds as well as whether it is to the free enzyme or the enzyme substrate complex. To get even more complicated there is another type of inhibitor that falls under the mixed category called noncompetitive, just a special case of mixed inhibitors. Each of these reversible inhibitors have a different effect on the Km and Vmax of the reaction which is key in terms of identifying which inhibitor is being used when looking at a graph.
Although enzymes can get complicated they are still an essential part of our cells and our bodies could not function properly without them!
Posted by Sarah Aboody (1) -second post