Biology Reference
In-Depth Information
nonnatural polysaccharides, and (3) achievement of green processes
without the use of harmful catalysts such as strong acids or bases
and heavy metals and the formation of byproducts.
Furthermore, the following two aspects should be emphasized
further as fundamental and important characteristics in enzymatic
reactions. The first is a “key and lock” theory proposed by Fischer
in 1984 [4], which points out the relation of enzyme to native
substrate. The theory implies that a specific substrate and an enzyme
correspond strictly in a 1:1 fashion like a key and lock relationship
in biosynthetic pathways. In the enzyme-substrate complex, the
substrate is located in the enzyme with geometrical adaptation,
leading to a product with perfect structural control. However, the key
and lock relationship observed for
enzymatic reactions is not
absolutely strict in many cases. Enzymes often have loose specificity
for recognition of the substrate structure and can insert with not
only a natural substrate but also a nonnatural one having the similar
structure as that of the former. In the case of
in vitro
enzymatic
synthesis of polysaccharides via nonbiosynthetic pathways, the
nonnatural substrate can be employed for the enzymatic catalysis.
The substrate is recognized by an enzyme to form a complex,
resulting in the progress of the desired reaction (Fig. 2.1).
The second characteristic for the enzymatic reaction is an energy
diagram. Pauling demonstrated in 1946 the reason why enzymatic
reactions proceed under the mild conditions [5]. The formation of
the enzyme-substrate complex stabilizes the transition state and
in vitro
Figure 2.1
The key and lock relationship for
in vitro
nonbiosynthetic
pathway.
