 In this video I will describe the characteristics and function of enzymes, describe the various factors that affect enzyme activity, including concentrations, temperature, pH, competitive inhibition, and allosteric regulation. An enzyme is a biological catalyst, and a catalyst is a chemical that will speed up a chemical reaction, but is not consumed in the chemical reaction, and therefore can be reused over and over again. An enzyme is typically made of protein, although some enzymes are made of nucleic acids, for example the ribosome has a catalytic region that's made out of RNA, but the majority of enzymes are proteins. An enzyme has an active site where the reagents will bind to the enzyme. These reagents are known as substrates, and the reagents or substrates will be converted into products as this chemical reaction proceeds. An enzyme is a catalyst and therefore enzymes speed up chemical reactions by lowering the activation energy required for that chemical reaction. The overall Gibbs free energy change of the chemical reaction is not affected by an enzyme, however by lowering the activation energy an enzyme can make a spontaneous chemical reaction, proceed more rapidly. Enzymes will also facilitate the coupling of endergenic reactions to exergenic reactions facilitating the non-spontaneous endergenic chemical reactions. Temperature influences the activity of an enzyme. This graph shows the activity of the enzyme represented in percentage of maximal activity on the y-axis, and temperature of the enzyme's environment on the x-axis. Enzymes will have the highest activity at an optimal temperature. If the temperature is lower than the optimal, there will be a lower rate of the chemical reaction. This is largely related to the decreased kinetic energy of molecules. As molecules are more slowly moving, it takes longer for those molecules to bind to the active site of the enzyme. If the temperature is higher than the optimal temperature for that enzyme, the reaction rate will also decline, but notice that there's a steep decrease once the temperature is greater than the optimal temperature. This graph is representing an enzyme that has its optimal temperature near body temperature of around 37 degrees Celsius. Once the enzyme is heated beyond its optimal temperature, it will start to change its shape and become misfolded. As the increased kinetic energy causes movement of the amino acids within the polypeptides of a protein for the enzyme, the enzyme can become misfolded and that is going to disrupt the function of the enzyme, changing the shape of the active site, preventing it from catalyzing the chemical reaction. So when a protein becomes misfolded as a result of an extreme environmental condition, that enzyme has become denatured. So denaturation is misfolding of a protein as a result of an extreme environmental condition. The example here that we see in the picture is frying of an egg. When you crack an egg, the egg white is primarily the protein ovalebumin that has a clear color to it, but as you expose that protein to an extreme environmental condition, very high temperature in the skillet, the ovalebumin protein will become misfolded, it will become denatured and that will lead to the opaque white color of the egg white when it cooks. When an enzyme is denatured, this will cause a change in the shape of the active site disrupting the function of the enzyme and so the structure of the enzyme is intimately connected to the function of the enzyme and a change in structure such as denaturation can disrupt the function. The concentration of hydrogen ions in the environment of an enzyme will also influence the enzyme's activity. Enzymes will have a highest activity at an optimal pH and if the environmental pH for that enzyme is lower or greater than the optimal pH, the enzyme activity will decrease. This is in part a result from hydrogen ions binding to the partial negative charges of polar covalent bonds and the negative charges from ionic side groups in the amino acid side chains of the polypeptide of the enzyme. As these hydrogen ions start to disrupt the interaction between charges that stabilize the secondary and tertiary structure of the enzyme, the enzyme can become misfolded and a misfolded or denatured enzyme will not be able to catalyze the chemical reaction. Enzymes function at an optimal pH that is typically the pH of the environment where they are functioning. For example, there are enzymes produced in our stomach that have an optimal pH of around two because the environment of the gastric juice in our stomach is a low pH whereas enzymes that function in our blood will have an optimal pH of around 7.4, the pH that's present in our blood and some enzymes will have an optimal pH that's much higher because they are operating in an environment with a relatively high pH. For example, the small intestines has a relatively high pH and there are many digestive enzymes secreted into the small intestine in order to facilitate digestion of food and these enzymes have an optimal pH of the higher pH typically found in the small intestines. Increasing the concentration of substrate will lead to an increased rate of the chemical reaction catalyzed by an enzyme until we reach saturation the maximum velocity or Vmax occurs when all of the enzyme in solution is saturated with substrate and therefore the chemical reaction will not accelerate if we increase the substrate concentration further as the enzymes are catalyzing the chemical reaction as rapidly as possible. The only way to create a further increase in the reaction rate would be to increase the concentration of enzyme inhibition of an enzyme is when a molecule known as an inhibitor binds to the enzyme and decreases the rate of the chemical reaction that is normally catalyzed by that enzyme. The graph here is showing us the relationship between substrate concentration and reaction rate of a normal solution containing enzyme with no inhibitor in the purple line compared to a competitive inhibitor in green and a non-competitive inhibitor in blue. A competitive inhibitor is a molecule that binds to the active site of the enzyme therefore as we increase the substrate concentration substrate will compete with the competitive inhibitor for the active site of the enzyme and at very high substrate concentration the substrate will out compete the inhibitor leading to the same Vmax as the solution with the normal enzyme that contains no inhibitor. In contrast a non-competitive inhibitor is a molecule that binds to a different location on the enzyme known as the allosteric site. Increasing the substrate concentration will increase the reaction rate of a solution that contains a non-competitive inhibitor however at very high substrate concentration a solution containing a non-competitive inhibitor will not reach the same Vmax as the solution that does not contain the non-competitive inhibitor. This is because the non-competitive inhibitor binding to an allosteric site will inactivate the enzyme preventing it from catalyzing the chemical reaction even though the active site may be able to bind to the substrate the enzyme will not catalyze the reaction. In some cases the non-competitive inhibitor binding to the allosteric site will change the shape of the enzyme so that the substrate cannot bind to the active site. Therefore increasing substrate concentration will only increase the activity of the enzymes that are not bound to a non-competitive inhibitor and all of the enzymes that have a non-competitive inhibitor bound are effectively removed from solution because they cannot catalyze the chemical reaction. So a non-competitive inhibitor can also be considered an allosteric inhibitor because a non-competitive inhibitor binds to a site that's different from the active site known as the allosteric site. In the illustration here you can see a non-competitive inhibitor binding to the allosteric site could change the structure of the enzyme preventing a substrate from binding to the active site. Some enzymes require allosteric activation where a molecule known as an activator binds to the allosteric site changing the structure of the enzyme which will enable the substrate to bind to the active site. Allosteric inhibition with a non-competitive inhibitor binding to an allosteric site is a common mechanism for feedback inhibition of a metabolic pathway where the end product functions as the non-competitive inhibitor binding to the allosteric site of the first enzyme in the metabolic pathway. This will help to control the concentration of the end product and prevent excessive amounts of substrate from entering the metabolic pathway. This will enable that substrate to enter other metabolic pathways or be saved until more end product is needed. Studying enzymes and enzyme inhibition has been useful clinically for the discovery of new medications. For example, aspirin is a medication that functions as an anti-inflammatory and pain reliever by inhibiting a cyclooxygenase enzyme involved in the pain and inflammation signaling pathways. However, medications often have side effects that can make them intolerable for some patients and they may work great for other patients. Studying the cyclooxygenase enzyme has led to the production of a variety of new non-steroidal anti-inflammatory medications that inhibit the cyclooxygenase enzyme. For example, ibuprofen and Advil and Aleve are non-steroidal anti-inflammatory medications that were discovered by looking for inhibitors of the cyclooxygenase enzymes.