MadSci Network: Biochemistry |
Many enzymes can exhibit a different pH optimum under different conditions. For example, the identity of the substrate can make a difference. The addition of cosolvents such as alcohols to the solution can affect the pH optimum for catalysis. For enzymes that utilize metal ions, the identity of the metal ions that are available can affect the pH optimum. Temperature can also make a difference. The presence of inhibitors can also make a difference. The question of why this happens can be complicated. When you determine the pH dependency you are actually titrating catalytic groups either on the substrate, on the enzyme, or on the enzyme-substrate complex. Any change in the experimental conditions, or in the nature of the substrate, that alters the pKa of one of the catalytic groups will result in a change in either the shape of the pH-rate dependency, or in the position of the pH optimum. Here is a web site that discusses the effect of pH on enzymatic activity: http://www.worthington-biochem.com/introBiochem/effectspH.html
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