Substrate (biochemistry)

Substrate (biochemistry)

A substrate in biochemistry is a molecule upon which an enzyme acts. Enzymes catalyze chemical reactions involving the substrate(s). In the case of a single substrate, the substrate binds with the enzyme active site, and an enzyme-substrate complex is formed. The substrate is transformed into one or more products, which are then released from the active site. The active site is now free to accept another substrate molecule. In the case of more than one substrate, these may bind in a particular order to the active site, before reacting together to produce products.

Substrate specificity

The substrate specificity of enzymes is a result of their unique three-dimensional structures. The "lock and key" model of enzyme-substrate interaction suggests that the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another. This model has been largely superseded, as it suggests a far too rigid enzyme structure and does not account for the inherent flexibility of proteins. The more recent "induced fit" model suggests that the enzyme structure is flexible and changes shape to fit the substrate.

Substrate concentration

The substrate concentration at which the enzyme activity is half of its maximal is the Michaelis-Menten constant, Km. The measure of the substrate's ability to be converted to product is termed the enzyme's turnover number, the number of substrate molecules an enzyme can convert per second.

See also

• Active site
• Enzyme catalysis
• Enzyme kinetics
• Enzyme inhibitor
• Michaelis-Menten kinetics

References

Substrate (biochemistry) Resources
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