Why is enzyme activity affected by ph

For single-substrate reactions the pH behavior of the parameters k 0 and k A can sometimes be represented by an equation of the form. The constants K 1 and K 2 can sometimes be identified as acid dissociation constants for the enzyme. The identification is, however, never straight forward and has to be justified by independent evidence. It is not accidental that this section has referred exclusively to pH dependences of k 0 and k A.

The pH dependence of the initial rate or, worse, the extent of reaction after a given time is rarely meaningful; the pH dependence of the Michaelis constant is often too complex to be readily interpretable. When using Representative Method As you might expect, this requirement places a serious limitation on kinetic methods of analysis. One solution to this problem is to stop, or quench the reaction by adjusting experimental conditions.

For example, many reactions show a strong pH dependency, and may be quenched by adding a strong acid or a strong base. Figure The reaction has a maximum rate at a pH of 5. Increasing the pH by adding NaOH quenches the reaction and converts the colorless p -nitrophenol to the yellow-colored p -nitrophenolate, which absorbs at nm. Kinetics The rates of enzyme-catalysed reactions vary with pH and often pass through a maximum as the pH is varied. The pH dependence of the Michaelis constant is often too complex to be readily interpretable.

Increasing the pH quenches the reaction and coverts colorless p-nitrophenol to the yellow-colored p-nitrophenolate, which absorbs at nm. The data are adapted from socrates. As with activity, for each enzyme there is also a region of pH optimal stability. In addition to temperature and pH there are other factors, such as ionic strength, which can affect the enzymatic reaction.

Each of these physical and chemical parameters must be considered and optimized in order for an enzymatic reaction to be accurate and reproducible. PDF version of Introduction to Enzymes.

Place Order. The rate of reaction will be affected, or the reaction will stop. A graph to show the effect of temperature on enzyme activity:. Enzymes are also sensitive to pH. Changing the pH of its surroundings will also change the shape of the active site of an enzyme.

Many amino acids in an enzyme molecule carry a charge. Within the enzyme molecule, positively and negatively charged amino acids will attract. This contributes to the folding of the enzyme molecule, its shape, and the shape of the active site. Changing the pH will affect the charges on the amino acid molecules.

Amino acids that attracted each other may no longer be. Again, the shape of the enzyme, along with its active site, will change. Extremes of pH also denature enzymes. The changes are usually, though not always, permanent. Enzymes work inside and outside cells, for instance in the digestive system where cell pH is kept at 7. Cellular enzymes will work best within this pH range. Different parts of the digestive system produce different enzymes.

These have different optimum pHs. The optimum pH in the stomach is produced by the secretion of hydrochloric acid. The optimum pH in the duodenum is produced by the secretion of sodium hydrogencarbonate.