Each enzyme works fastest at a particular pH, its optimum pH. Most intracellular enzymes have an optimum near pH 7, but some differ:
• pepsin, a protease in the stomach: about pH 2
• salivary amylase: about pH 7
• trypsin in the small intestine: about pH 8
• it alters the charges on the R groups of amino acids in the active site, so the substrate may no longer bind or the reaction may not be catalysed
• it disrupts the ionic bonds and hydrogen bonds that hold the tertiary structure, changing the shape of the active siteSmall changes either side of the optimum reduce the rate but are usually reversible. At extreme pH values the tertiary structure is changed so much that the enzyme is denatured.In experiments, pH is controlled with a buffer solution, which resists changes in pH.The pH scale is logarithmic: a fall of one pH unit means a tenfold increase in H+ concentration.Worked example: a solution at pH 4 has 10 × 10 = 100 times the hydrogen ion concentration of a solution at pH 6.
• pepsin, a protease in the stomach: about pH 2
• salivary amylase: about pH 7
• trypsin in the small intestine: about pH 8
• it alters the charges on the R groups of amino acids in the active site, so the substrate may no longer bind or the reaction may not be catalysed
• it disrupts the ionic bonds and hydrogen bonds that hold the tertiary structure, changing the shape of the active siteSmall changes either side of the optimum reduce the rate but are usually reversible. At extreme pH values the tertiary structure is changed so much that the enzyme is denatured.In experiments, pH is controlled with a buffer solution, which resists changes in pH.The pH scale is logarithmic: a fall of one pH unit means a tenfold increase in H+ concentration.Worked example: a solution at pH 4 has 10 × 10 = 100 times the hydrogen ion concentration of a solution at pH 6.