Temperature, activators, pH levels, and inhibitors are just a few of the variables that might influence enzyme activity. That's a nice one, temperature. Proteins alter form when temperatures rise and fall. Some proteins lose their structure completely at 56 degrees Fahrenheit (13 degrees Celsius). Other proteins remain functional but may show altered behavior at that temperature. Enzymes are proteins too, so they will change form as well.
Enzymes are activated by other proteins called "activators." These molecules often bind to enzymes at specific sites and help them gain access to their substrate molecules. For example, an enzyme called phosphorylase binds to phosphorylated sugars to create phospho-sugars. The phosphorylase then leaves its binding site on the sugar molecule and allows another enzyme called glycogen synthase to attach to the phosphate group. This step is necessary before the sugar can be used for storage in cells when phosphorylation causes it to be ignored by other enzymes.
An inhibitor binds to an enzyme at a site where an activator would go and blocks it from acting on its substrate. For example, an enzyme called pyruvate kinase cannot use phospho-sugars as substrates until it has been activated by adding a phosphate group.
Temperature, pH, and concentration are all parameters that can influence enzyme activity. Enzymes function best in specified temperature and pH ranges, and poor circumstances can lead an enzyme to lose its ability to bind to a substrate. The more concentrated the solution, the faster certain enzymes will act.
Enzymes are proteins. Like other proteins, their structure is stabilized by the arrangement of amino acids into chains. Amino acids can be classified as either acidic or basic, based on their chemical properties. An acid residue has a hydrogen atom attached to a carboxyl group (carbon dioxide) while a base residue has a hydroxyl group attached to a nitrogen atom. Acidic residues include Asp, Glu; basic residues include Lys, Arg. Enzymes contain both types of residues in various amounts. When an enzyme binds to a substrate, an ion pair is formed. The positive charge of the enzyme is balanced by the negative charge of the substrate. This interaction keeps the enzyme active long enough for another molecule of substrate to reach it.
Enzymes are important tools used by living organisms to break down complex molecules into simpler ones that can be used for energy storage or reproduction. In humans, enzymes control many processes inside our bodies. They are also used in food processing and medicine. Uncontrolled enzymes can be dangerous, so cells contain mechanisms to inhibit them when necessary.
Raising the temperature often accelerates a process, whereas lowering the temperature slows it down. Extremely high temperatures, on the other hand, can cause an enzyme to lose its form (denature) and cease to function. Enzymes are very sensitive to changes in pH; at some points on their curve, enzymes are most active when the pH is exactly right for them to be maximally efficient.
The maximum possible concentration of an enzyme in solution is called its "saturation level." Adding more enzyme will not increase the rate at which it catalyzes a reaction; instead, another site on the enzyme becomes saturated and no further reaction takes place. Saturation levels can be increased by any one of three methods: increasing the amount of substrate available to the enzyme, decreasing the amount of inhibitor present, or changing the environment such that it no longer inhibits the enzyme.
At some point, increasing the saturation level any further won't change the rate at which the enzyme reacts. This is because at high concentrations many substrate molecules overlap with each other, preventing additional reactions from occurring. The enzyme can no longer interact efficiently with one molecule of substrate per time interval so the rate of reaction slows down. At this point, more enzyme doesn't help the reaction proceed any faster - it only consumes extra energy to produce more product! This is why enzyme activity levels off as the concentration increases.
PH: Each enzyme has a preferred pH range. Changing the pH outside of this range will cause enzyme activity to slow down. Concentration: At some point, increasing the amount of substrate will no longer result in more product, because the enzymes become saturated.