Elementary plant Biochemistry and Biotechnology (2+1)

Enzymes – classification, Mechanism of enzyme action –active site

One of the unique characteristics of a living cell is its ability to permit complex reactions to proceed rapidly at the temperature of the surrounding environment.

• The principal agents which participate in the remarkable transformations in the cell belong to a group of proteins named enzymes. In the absence of enzymes in the cell, these reactions would proceed too slowly.
• Enzymes are proteins specialised to catalyse biological reactions with the following characteristics

Characteristics of enzymes

• Enzymes being proteins exhibit all properties of protein.
• They have their specific isoelectric points at which they are least soluble.
• Like proteins, they can be denatured by changes in pH and temperature.
• The enzyme-catalysed reactions occur below 100oC, at atmospheric pressure and nearby neutral pH.
• Enzymes undergo physical changes during the reaction but revert to their original form at the end of the reaction.Enzymes exhibit enormous catalytic power.
• The rates of enzymatically catalysed reactions are 106 - 1012 times greater than those of the corresponding uncatalysed reactions and several times greater than those of the corresponding chemically catalysed reactions.
• For example the carbonic anhydrase enzyme catalyses the conversion of carbondioxide to carbonic acid
CO2 + H2O . H2CO3

• In this reaction, each enzyme molecule can hydrate 105 molecules of CO2 per second.
• Enzyme activity is regulated in a variety of ways, ranging from controls over the amount of enzyme protein synthesised by the cell or modulation of activity through reversible interaction with metabolic inhibitors and activators or through isoenzymes.