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|Chapter Two: The Chemistry of Biology|
There are a number of influences than can change the efficiency of enzyme. We will discuss the four most important factors: inhibitors, allosteric factors, pH, and temperature.
There are two types of inhibitors: competitive inhibitors and noncompetitive inhibitors, and their names give a good indication of what they actually do. Competitive inhibitors have a similar structure to the enzyme's substrate, so they can "compete" with the substrate for the active site of an enzyme. Often the enzyme will bond not to its substrate but to the competitive inhibitor, blocking the substrate from the active site and causing the formation of enzyme-substrate complexes to occur at a slower rate. Noncompetitive inhibitors, on the other hand, do not attach to the active site and block the enzyme-substrate complex from forming. Instead, they react with portions of the active site, which results in the changing of its shape. Once the active site's shape is changed, it can no longer attach to the substrate.
Some enzymes have special areas other than the active site. These special areas are sometimes called regulatory sites. Any molecule that attaches to the regulatory site is called an allosteric factor. Allosteric inhibitors join with the regulatory site and change the shape of the entire enzyme (including the active site), thus preventing it from binding with the substrate. However, not all allosteric factors are detrimental. Some join with the regulatory site and actually bring the enzyme and its active site into the proper shape so that it can successfully form enzyme-substrate complexes.
pH also plays an important role in affecting the rate of an enzyme's activity. Remember that pH is a measure of how acidic or basic a solution is; that is, how many H+ or OH- ions there are. These ions are charged, and charged molecules tend to pull on other molecules. So, if too many ions are present, the enzyme may be denatured (twisted and pulled so out of shape that it can no longer function). However, this is not to say that all enzymes work best when the pH is neutral. Some enzymes actually work best in acidic or basic environments, but these characteristics are particular to the enzyme.
The final factor that influences an enzyme's efficiency is temperature. To a certain extent, a high temperature increases the rate of an enzyme's activity, because at high temperatures, molecules move around faster, so an enzyme is likely to come in contact with a substrate very quickly. However, at too high temperatures, the enzyme can become denatured and lose all function. Low temperatures slow the rate of formation of the enzyme-substrate complex because the molecules move at slower speeds and so do not come in contact with one another as frequently.