Enzyme :: essays research papers

The plot of enzyme activity Vs. pH is often "bell shaped" since two different amino acid groups of the enzyme are being titrated to different states of ionization at the different pH values. This means that only one of the two possible ionization states of the amino acid side chain is effective in enzyme catalysis - in other words, if an acidic side chain like Glu is involved in catalysis, it probably only works when it is ionized; since Glu side chain carboxylic acid groups have a pK around pH 5, at pH values below this pK, the enzyme will be less active; while at pH values above the pK, the enzyme will be most active. At higher pH values, another group, for example, the amino side chain group in a Lys may control the activity. So at pH values below the pK of the Lys amino side chain, which is about pH 9, the enzyme is active, while at pH values above the Lys side chain pK, the enzyme will be less active. In the end, the pH optimum lies somewhere between the pK values for these two groups that control the enzyme's activity. B. Temperature Optimum Most enzymes have an optimum temperature, which may be related to the type of organism from which the enzyme was isolated. Some organisms like plants grow well near room temperature and so their enzymes are most active at a temperature around 30 to 40Â °C. A general rule of thumb from chemistry is that a reaction's rate approximately doubles with a 10Â °C increase in reaction or assay temperature. However, since enzyme are held together by weak non-covalent bonds, at higher temperatures, the enzyme catalyzed rate slows down rather than increases: Of courese, at low temperatures, all the molecules in the solution slow down and so does the enzyme catalyzed reaction. At high temperatures, the thermal movement of the molecules become to great for the enzyme to hold its shape or conformation and so it begins to denature and lose its activity. Animal enzymes often have temperature optima near 37Â °C (especially human's since this is body temperature). For thermophilic organisms, like ba cteria or blue-green algae which grow well in near boiling hot springs, much higher temperature optima are found; some enzymes even have temperature optima near 90Â °C. In the end, the temperature you use for an enzyme assay may depend on the equipment available to you in the lab.