Elementary plant Biochemistry and Biotechnology (2+1)

4.pH

pH

•Most enzymes have a characteristic pH at which their activity is maximum; above or below this pH, the activity declines
•The pH affects the ionic state of the enzyme and frequently that of the substrate also.
•If a negatively charged enzyme (E-) reacts with a positively charged substrate (SH+), ESH is formed.
•At low pH values, E- will be protonated and ESH is not formed.
Similarly, at very high pH values SH+ will ionize and lose its positive charge.

E- + SH+ →ESH
acidic pH
E- + SH+ → EH + SH+ → No ESH formation
alkaline pH
SH+ → S + H+ + E- → No ESH formation

•Another important factor is the change in conformation (denaturation) of enzyme at extreme pH values.