Denniston, 7e
Glossary of Key Terms in Chapter Nineteen
absolute specificity (19.5) the property of certain enzymes that allows them to bind and catalyze the
reaction of only one substrate.
active site (19.4) the cleft in the surface of an enzyme that is the site of substrate binding.
allosteric enzymes (19.9) enzymes that have an effector binding site as well as an active site; effector
binding changes the shape of the active site, rendering it either active or inactive.
apoenzyme (19.7) the protein portion of an enzyme that requires a cofactor in order to function in
catalysis.
coenzyme (19.7) an organic group required by some enzymes; generally a donor or acceptor of electrons
or functional groups in a reaction.
cofactor (19.7) metal ions, organic compounds, or organometallic compounds that must be bound to an
apoenzyme to maintain the correct configuration of the active site.
competitive inhibitor (19.10) a structural analog; a molecule that has a structure very similar to the
natural substrate of an enzyme, competes with the natural substrate for binding to the enzyme active
site, and inhibits the reaction.
enzyme (Intro) a protein that acts as a biological catalyst.
enzyme specificity (19.5) the ability of an enzyme to bind to only one, or a very few, substrates and thus
catalyze only a single reaction.
enzyme-substrate complex (19.4) a molecular aggregate formed when the substrate binds to the active
site of the enzyme.
feedback inhibition (19.9) when produced in excess, the product of a biosynthetic pathway can turn off
the entire pathway for its own synthesis. This is an example of negative allosterism. The product of
the pathway is a negative allosteric effector of one of the enzymes early in the pathway.
group specificity (19.5) the property of certain enzymes that allows them to catalyze reactions involving
similar substrate molecules having the same functional groups.
holoenzyme (19.7) an active enzyme consisting of an apoenzyme bound to a cofactor.
hydrolase (19.1) an enzyme that catalyzes a hydrolysis reaction.
induced-fit model (19.4) the theory of enzyme-substrate binding that assumes that the enzyme is a
flexible molecule and that both the substrate and enzyme change their shapes to accommodate one
another as the enzyme-substrate complex forms.
irreversible enzyme inhibitor (19.10) a chemical that binds strongly to the R groups of an amino acid in
the active site and eliminates enzyme activity.
isomerase (19.1) an enzyme that catalyzes the conversion of one isomer to another.
ligase (19.1) an enzyme that catalyzes the joining of two molecules.
linkage specificity (19.5) the property of certain enzymes that allows them to catalyze reactions involving
only one kind of bond in the substrate molecule.
lock-and-key model (19.4) the theory of enzyme-substrate binding that describes enzymes as inflexible
molecules and a substrate that fits into the rigid active site in the same way a key fits into a lock.
lyase (19.1) an enzyme that catalyzes a reaction involving double bonds.
negative allosterism (19.9) effector binding inactivates the active site of an allosteric enzyme.
oxidoreductase (19.1) an enzyme that catalyzes oxidation-reduction reactions.
pancreatic serine proteases (19.11) a family of enzymes, including trypsin, chymotrypsin, and elastase,
that hydrolyze dietary proteins in the small intestine.
pH optimum (19.8) the pH at which an enzyme catalyzes the reaction at maximum efficiency.
positive allosterism (19.9) effector binding activates the active site of an allosteric enzyme.
product (19.2) the chemical species that results from an enzyme-catalyzed reaction.
proenzyme (19.9) the inactive form of a proteolytic enzyme
protein modification (19.9) a means of enzyme regulation in which a chemical group is covalently added
or removed from a protein; the chemical modification either turns the enzyme on or turns it off.
proteolytic enzyme (19.11) an enzyme that hydrolyzes the peptide bonds between amino acids in a
protein chain.
reversible, competitive enzyme inhibitor (19.10) a chemical that resembles the structure and charge
distribution of the natural substrate and competes with it for the active site.
reversible, noncompetitive enzyme inhibitor (19.10) a chemical that binds weakly to an amino acid R
group or cofactor and inhibits activity. When the inhibitor dissociates, the enzyme is restored to its
active form.
stereochemical specificity (19.5) the property of certain enzymes that allows them to catalyze reactions
involving only one enantiomer of the substrate.
structural analog (19.10) a chemical having a structure and charge distribution very similar to a natural
enzyme substrate.
substrate (19.1) the reactant in a chemical reaction that binds to the enzyme active site and is converted to
the product.
temperature optimum (19.8) the temperature at which an enzyme functions optimally and the rate of
reaction is maximal.
transferase (19.1) an enzyme that catalyzes the transfer of a functional group from one molecule to
another.
transition state (19.6) the unstable intermediate in catalysis in which the enzyme has altered the form of
the substrate so that it now shares properties of both the substrate and the product.
vitamin (19.7) an organic substance that is required in the diet in small amounts; water-soluble vitamins
are used in the synthesis of coenzymes required for the function of cellular enzymes; lipid-soluble
vitamins are involved in calcium metabolism, vision, and blood clotting.