hydrolase
Summary
A hydrolase is an enzyme that cleaves a bond by adding water across it; proteases, lipases, nucleases, phosphatases and amylase are examples. Testable point: hydrolases use water, while lyases cleave without water or oxidation and ligases join molecules, usually using ATP.
Detail
Meaning: A hydrolase catalyzes hydrolysis, cleaving a covalent bond by adding water: OH goes to one product and H to the other. Hydrolases are one of the six enzyme classes. Examples: proteases (peptide bonds), lipases (esters), nucleases (phosphodiester bonds), phosphatases (phosphate esters), and amylase (glycosidic bonds). The enzyme speeds the reaction but does not change ΔG.
Equation: R–R′ + H₂O → R–OH + R′–H, where R and R′ are the two parts of the substrate and H₂O is the water consumed. These are chemical species, so no SI unit applies beyond amounts in mol.
On the MCAT: You may be asked to classify an enzyme from its reaction ("cleaves a peptide bond using water" means hydrolase), or to work through digestion passages involving proteases, lipase, and amylase.
Common confusion: Lyases also break bonds, but without water or redox, often leaving a double bond. A kinase transfers phosphate from ATP, and phosphorylase uses inorganic phosphate, so neither is a hydrolase. A phosphatase removes phosphate using water, so it is.
Sources
- Lehninger Principles of Biochemistry
- Biochemistry (Berg, Tymoczko, Stryer)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.