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Basic Theory Behind Enzymes
Enzyme ¡V biological catalyst . The term enzyme comes from
zymosis, the Greek word for fermentation , a process
accomplished by yeast cells and long known to the brewing
industry, which occupied the attention of many 19th-century
chemists. Louis Pasteur recognized in 1860 that enzymes
were essential to fermentation but assumed that their
catalytic action was inextricably linked with the structure
and life of the yeast cell. Not until 1897 was it shown by
German chemist Edward Büchner that cell-free extracts of
yeast could ferment sugars to alcohol and carbon dioxide;
Büchner denoted his preparation zymase. This
important achievement was the first indication that enzymes
could function independently of the cell.
The
first enzyme molecule to be isolated in pure crystalline
form was urease, prepared from the jack bean in 1926 by
American biochemist J. B. Sumner, who suggested, contrary to
prevailing opinion, that the molecule was a protein . In the
period from 1930 to 1936, pepsin , chymotrypsin , and
trypsin were successfully crystallized; it was confirmed
that the crystals were protein, and the protein nature of
enzymes was thereby firmly established.
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Figure 1: 3D Structural Diagram of an £\-Amylase |
An
enzyme is a protein, or protein complex, that catalyzes a
chemical reaction without the enzyme itself being altered,
and also controls the 3D orientation of the catalyzed
substrates. Like any catalyst, enzymes work by lowering the
activation energy of a reaction, thus allowing the reaction
to proceed to its steady state or completion much faster
than it otherwise would. Enzymes may speed up biochemical
reactions by a factor of many thousand times, often by
several orders of magnitude.
Catalysis by an enzyme is analogous to removing a pebble
that is stopping the ball from rolling down the hill; the
reaction goes to completion more quickly, but the final
product is identical. An enzyme contains one or more
binding sites where the substrate(s) attach, and active
site(s), where the amino acids perform the catalysis; and
frequently one or more other binding sites that serve
regulatory functions, which increase or inhibit the enzyme's
activity. Enzymes are usually specific as to the reactions
they catalyze and the substrates that are involved in these
reactions. Complementary structural properties of the enzyme
and substrate are responsible for this specificity.
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Figure 2: Diagram of a catalytic reaction, showing
the energy needed at each stage of the reaction. The
substrates (A and B) normally need a large amount of
energy to reach the transition state, which then
reacts to form the end product (AB). The enzyme
forms a microenvironment in which A and B can reach
the transition state more easily, reducing the
amount of energy required. Since the lower energy
state is easier to reach and therefore occurs more
frequently, as a result the reaction is more likely
to take place, thus improving the reaction speed.
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Most enzymatic reactions occur
within a relatively narrow temperature range
(usually from about 30¢XC to 40¢XC), a feature that
reflects their complexity as biological molecules.
Each enzyme has an optimal range of p H for
activity; for example, pepsin in the stomach has
maximal reactivity under the extremely acid
conditions of p H 1-3. Effective catalysis
also depends crucially upon maintenance of the
molecule's elaborate three-dimensional structure.
Loss of structural integrity, which may result from
such factors as changes in pH or high
temperatures, almost always leads to a loss of
enzymatic activity. An enzyme that has been so
altered is said to be denatured, meaning it as lost
its native, higher-order structure of protein
molecules in solution. Most globular proteins
exhibit complicated three-dimensional folding
described as secondary, tertiary, and quarternary
structures.
Figure 3:
Bacteria Culture dedicated to the production of
ZDSS's Acidic Protease
These conformations of the protein molecule are
rather fragile, and any factor that alters the
precise geometry is said to cause denaturation.
Thus, the denatured enzyme is often without
catalytic function. Renaturation is accomplished
with varying success, and occasionally with a return
of biological function, by exposing the denatured
protein to a solution that approximates normal
physiological conditions.
Consonant with their role as biological catalysts,
enzymes show considerable selectivity for the
molecules upon which they act (called substrates).
Most enzymes will react with only a small group of
closely related chemical compounds; many demonstrate
absolute specificity, having only one substrate
molecule which is appropriate for reaction. |
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