Enzyme specificity limits the range of action of a certain enzyme enzyme. We distinguish two types of specificity:
1. Substrate specificity[edit | edit source]
The enzyme acts only on a limited group of substrates and will not catalyze the reaction for other substrates. Depending on the extent, substrate specificity can be:
Absolute:[edit | edit source]
- The enzyme catalyzes the reaction of only one specific substrate, but will no longer catalyze reactions involving, for example, derivatives of this substrate. An example is urease catalyzing the reaction:
- urea + H2O → CO2 + 2 NH3
- However, urease cannot catalyze the hydrolysis of methylurea or thiourea.
Group:[edit | edit source]
- This is a more common form of specificity. An enzyme catalyzes the reaction of several similar substrates (typically containing the same functional groups). The affinity for each substrate can be different (KM therefore differs for individual substrates). An example is carboxypeptidase B, which hydrolyzes peptides from their carboxy-terminus. It preferentially cleaves peptide bonds containing charged amino acids (arginine, lysine).
2. Reaction (effect) specificity[edit | edit source]
Many enzymes act stereospecifically. They attack only certain configurational isomers of the (for example only the L- or only the D- form) probably due to the necessity of binding the substrate to at least three specific sites of the active center of the enzyme (which is a chiral compound) – the opposite stereoisomer does not bind.