Properties of Enzyme:
- Enzymes are generally globular proteins. Being proteinaceous, the enzymes are giant molecules with a
molecular weight of 6000 (bacterial ferredoxin) to 4,600,000 (pyruvate dehydrogenase complex).
Eg. Lysozyme - The primary structure of lysozyme is a single polypeptide containing 129 amino acids.
In physiological conditions, lysozyme is folded into a compact, globular structure with a long cleft in the
protein surface. This cleft is the active site involved in binding to the bacterial carbohydrate chain and
subsequently cleaving it. (Fig) - Enzymes are Thermolabile, Colloidal in Nature, reversible and highly specific.
- Enzymes act as catalysts i.e., they do not start a chemical reaction but increase the rate of chemical
reaction. - Efficiency: The number of substrate molecules changed per minute by a molecule or enzyme is called
turn over number (kcat). The higher the turn-over number, the more efficient an enzyme is. It depends
upon the number of active points present over an enzyme, precise collisions between reactants and the
rate of removal of end products. - pH: Each enzyme functions at a particular pH called optimum pH e.g., pepsin (2 pH), sucrase (4.5 pH),
salivary amylase (6.8 pH), trypsin (8.5 pH). A change in pH makes the enzymes ineffective. - Temperature: Each enzyme functions at a particular temperature called optimum temperature.
- The rate of a biochemical reaction rises with the increase in enzyme concentration up to a point called
limiting or saturation point. Beyond this, increase in enzyme concentration has little effect. - Increasing the concentration of reactants (substrates) increases the rate of reaction by increasing the
frequency with which substrate molecules collide with enzyme molecules. If the concentration of substrates
is increased beyond a certain point, called the point of saturation, then there will not be a further increase in
enzyme activity since the enzymes would already be contacting substrates at the maximum rate possible.
Fig: Factors affecting enzyme activity
- As the temperature increases there is more movement of molecules and therefore more collisions between
enzymes and substrates – so the enzyme activity increases. However, there is a limit to which enzyme
activity can increase because at a certain temperature an enzyme will denature. - When the pH is too acidic or too basic for an enzyme, its hydrogen bonds begin to break, causing its active
site to change its shape. An altered active site can’t bind with its substrate so enzyme activity decreases. If
the pH is too unfavourable then covalent bonds can break, causing the enzyme to denature.