BOTANY Higher Secondary Second Year - Textbooks Online

Isomerases
The enzymes that catalyzes rearrangement of atoms within a molecule
to form isomers are called isomerases. eg. phosphohexoisomerase.
Ligases
Ligases catalyze the formation of C – C, C – S, C – O and C – N
bonds. The energy for the reaction is derived by the hydrolysis of ATP.
eg. pyruvate carboxylase.
5.1.2. Properties of enzymes
Like inorganic catalysts, the enzymes are active in very small amounts
and remain unchanged on completion of the reaction.
Enzymes are very specific in their action. i.e. a particular enzyme
usually acts on a particular substrates to catalyze particular type of
reaction. But some times, the same reaction may be catalyzed by
more than one enzyme. Such enzymes are called isoenzymes.
Enzymes are very sensitive to heat. The temperature at which an
enzyme shows its highest activity is called optimum temperature. The
activity of enzyme declines both the above and below the optimum
temperature. Protein part of the enzyme is the catalytic part.
Temperature above 50°C normally denatures the protein and so the
enzyme loses its activity.
The catalytic property of the enzyme is dependent on pH. The specific
pH at which the enzyme activity is high is called optimum pH. Different
types of enzymes have different optimum pH values. Most intracellular
enzymes function will be around neutral pH. Tripsins are active in
alkaline medium, diastase in neutral medium while pepsin in acidic
medium.
Enzymes are sensitive to inhibitors. The chemical substance that
combines with the enzymes and inhibits its catalytic activity is called
an inhibitor. eg. Cyanides.
In most of the cases, the reactions catalyzed by the enzymes are
reversible depending upon the requirements of the cell.
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