Enzyme Specificity vs Selectivity

biochemistry enzymes

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Solution 1

Specificity is the term used to define the selectivity of enzymes for their substrates. The selective qualities of an enzyme are collectively recognized as its specificity.

Other texts have synonymised enzyme selectivity with substrate specificity:

The non-covalent forces through which substrates and other molecules bind to enzymes are similar in character to the forces that dictate the conformations of the proteins themselves : Both involve van der Waals, electrostatic, hydrogen bonding, and hydrophobic interactions. Molecules that differ in shape or functional group distribution from the substrate cannot productively bind to the enzyme; that is, they cannot form enzyme–substrate complexes that lead to the formation of products.

The extraordinary ability of an enzyme to catalyse only one particular reaction is a quality known as specificity.

Specificity means an enzyme acts only on a specific substance, its substrate, invariably transforming it into a specific product. That is, an enzyme binds only certain compounds, and then, only a specific reaction ensues. Some enzymes show absolute specificity, catalyzing the transformation of only one specific substrate to yield a unique product. Other enzymes carry out a particular reaction but act on a class of compounds. For example, hexokinase (ATP-hexose-6- phosphotransferase) will carry out the ATP-dependent phosphorylation of a number of hexoses at the 6-position, including glucose.

Pioneering enzyme specificity studies at the turn of the 20th century by the great organic chemist Emil Fischer led to the notion of an enzyme resembling a “lock” and its particular substrate the “key.” The specificity of an enzyme (the lock) for its substrate (the key) arises from their geometrically complementary shapes. This was later modified to a more accurate induced fit hypothesis given the high flexibility, conformationally dynamic properties of enzyme molecules.

References

Voet and Voet Biochemistry 4th ed: Introduction to Enzymes
Biochemistry Grisham & Garret How Can Enzymes Be So Specific?

Solution 2

Selectivity is used when talking about the substrate, for example an enzyme can be more selective for D- sugars compared to L-sugars.

Specificity is used when talking about the product. For example an enzyme that only accepts a single compound could specifically hydroxylate the 2 position, even though there are be more positions that could be hydroxylated.

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EdL

Updated on August 01, 2022

Comments

EdL over 1 year

Background: I can see a difference in stereoselective and stereospecific reactions in organic chemistry. However, both terms are used interchangeably as synonyms in a biochemistry class.

Question: What differs selectivity from specificity in enzymatic reactions. What is meant when we talk about enzyme specificity and enzyme selectivity?