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Paschal Ejims

Enzyme Specificity vs Selectivity

Chris Mansker  Follow

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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Catherine Shoff  Follow

Specificity is the term used to define the selectivity of enzymesfor 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 forcesthat dictate the conformations of the proteins themselves : Both involve van der Waals, electrostatic, hydrogenbonding, and hydrophobic interactions.Molecules that differ in shape or functional group distributionfrom the substrate cannot productively bind to theenzyme; that is, they cannot form enzyme–substrate complexesthat 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 enzymebinds only certain compounds, and then, only a specific reaction ensues.Some enzymes show absolute specificity, catalyzing the transformation of only onespecific substrate to yield a unique product. Other enzymes carry out a particularreaction but act on a class of compounds. For example, hexokinase (ATP-hexose-6-phosphotransferase) will carry out the ATP-dependent phosphorylation of a numberof hexoses at the 6-position, including glucose.

Pioneering enzyme specificity studies at the turn of the 20th centuryby the great organic chemist Emil Fischer led to the notion of anenzyme 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 latermodified to a more accurate induced fit hypothesis given the highflexibility, conformationally dynamic properties of enzyme molecules.

References

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

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