A Webpage by Chul-Won Park and Erik Zipp
for Introduction to Biochemical Engineering, Fall 2000.
An enzyme is a protein-based substance which serves as a catalyst in
living organisms by regulating the rate of spontaneously chemical
reactions. The rate of reaction does not solely depend on the free energy
difference between the initial and final states, but instead on the actual
path through which the reactants are transformed into products. Without
these catalysts, simple tasks that occur within living organisms cannot
take place at a rate beneficial to the species. The enzymes increase the
rate of reaction without effecting the reactions difference in free
energy. Natural mechanisms such as the digestion of food, the conservation
and transformation of chemical energy, and the construction of cellular
macromolecules from smaller precursors are all supported with the use of
enzymes. In fact, if a living organism is deficient in a particular
enzyme, it could result in serious diseases and possibly death.
Enzymes also act in industrial and medical applications. The fermenting
of wine, leavening of bread, the curdling of cheese, and the brewing of
beer have been practiced for centuries, but it wasn't until recently that
all these processes have been discovered to be possible with the use of
enzymes. Once discovered to be beneficial to industrial use, enzymes have
found their way into many applications, with none more important than the
production of man-made pharmacutical drigs which can kill disease-causing
microorganisms, promote wound healing, and even diagnosing certain
potentiaklly life-threateneing diseases.
How do ENZYMES work?
General Properties of ENZYMES.
Enzymes promote the rate of reactions in several ways.
However, all these properties of enzymes are dependent on the external
environment of the reaction. Temperature and pH both effect the rates at
which a reaction takes place, and there exists an optimum value for each.
Effects of pH on ENZYMES.
Most proteins, and therefore enzymes, are active only within a narrow
pH range usually between 5 and 9. Several factors are influenced directly
by the pH in which the reaction takes place.
The graph of pH against the reaction rate is a bell shaped curve. The
curve reprecents the ionization of certain amino acid residue that must be
in a specific ionization state for enzyme activity. The inflection point
of the curve is called the pK of the reaction and can identify amino acid
residues essential to enzymatic activity.
Effects of Temperature on ENZYMES.
Temperature can effect an enzyme in two ways. One is a direct influence
on the reaction rate constant, and the other is in thermal denturization
of the enzyme at elevated temperatures.
To relate the effect of temperature to the reaction rate constant, the
Arrhenius equation is used:
where k is the rate constant, R is the gas law constant, A is the frequency factor and Ea is the activation energy of the reaction.
The temperature range over which enzymes show activity is limited between the melting point (0oC) and bioling point (100oC) of water. If a temperature is too low, there can be no noticable reaction rate since the enzyme is operating at a temperature far below its optimum. If the temperature at which the enzyme is operating at is well above 100oC, then thermal deactivization can occur.
Thermal deactivization of enzymes limits their useful lifetime in
processing environments. Therefore, it is important in many preocess
design and manufacturing levels to have the correct temperature of
reaction. If the reaction temperature is too high, the enzymes will
eventually deactivate in an irreversible way and thus halting the reaction
from taking place. For many enzymes found within mammals, the optimum
temperature is 37oC, but deactivization can occur as low as 45
to 55oC. Deactivization of enzymes may be irreversible or
All pictures (C) Voet, Voet and Pratt, Fundamentals of Chemistry, John Wiley & Sons, Inc. 1999
References: Voet, Voet and Pratt, Fundamentals of Chemistry, John Wiley & Sons, Inc. 1999
Blanch and Clark, Biochemical Engineering, Marcel Dekker, Inc. 1997.