Page 10 - 11-Bio-3 Enzymes
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3. Enzymes eLearn.Punjab
Table 4.1 Optimum pH values for some enzymes
Enzyme Optimum pH
Pepsin 2.00
4.50
Sucrase 5.50
6.80
Enterokinase 7.60
Salivary amylase
Catalase 7.00-8.00
Chymotrypsin
Pancreatic lipase 9.00
Arginase 9.70
Inhibitors
An inhibitor is a chemical substance which can react (in place of substrate) with the enzyme but
is not transformed into product(s) and thus blocks the active site temporarily or permanently, for
example poisons, like cyanide;, antibiotics, anti-metabolites and some drugs.
Inhibitors can be divided into two types: (i) Irreversible (ii) Reversible
Irreversible Inhibitors
They check the reaction rate by occupying the active sites or destroying the globular structure.
They occupy the active sites by forming covalent bonds or they may physically block the active sites.
Reversible Inhibitors
They form weak linkages with the enzyme. Their effect can be neutralized completely or partly by
an increase in the concentration of the substrate.
They are further divided into two major types: A. Competitive B. Non-competitive
A. Competitive Inhibitors
Because of the structural similarity with the substrate they may be selected by the binding sites,
but are not able to activate the catalytic sites. Thus product(s) are not formed (Fig.3.6).
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