enzyme
a macromolecule, mostly of protein nature, that function as biocatalyst by increasing the
reaction rate
catalyst
a substance that increases the rate of a reaction without modifying the overall standard
Gibbs energy change in the reaction; the catalyst is both a reactant and product of the
reaction; the process is called catalysis
-ase
the ending denoting an enzyme molecule (e.g. kinase, lactase, peroxidase)
substrate
the chemical entity whose conversion to a product or products is catalysed by one or
several enzymes
active site
(active center)
the effective site for a particular catalytic reaction (the site at which a catalytic reaction
takes place)
binding site
a specific region in a molecule (enzyme) that is capable of entering into a stabilizing
interaction with another molecule (substrate); typical forms of interaction are by
hydrogen bonding, coordination and ion pair formation
enzyme specificity
the degree to which an enzyme will catalyze one or more reactions

reaction specificity an enzyme catalyses only one rection type

substrate
specificity
an enzyme operates on only one type of substrate (group of similar substrates) and
preferentially one of the enantiomers of chiral substrates is attacked
cofactors
organic molecules or ions (usually metal ions) that are required by an enzyme for its
activity; they may be attached either loosely (coenzyme) or tightly (prostetic group) to
the enzyme; a cofactor binds with its associated protein (apoenzyme), which is
functionally inactive, to form the active enzyme (holoenzyme)
coenzyme
the dissociable, low-relative-molecular-mass active group of an enzyme which transfers
chemical groups, hydrogen or electrons
prostetic group
the non-amino acid portion of a conjugated protein (= general definition of the term)
vitamin
one of a number of organic compounds required by living organisms in relatively small
amounts to maintain normal health; vitamins or their derivatives function typically as
coenzymes (they are precursors of coenzymes)
apoprotein
a protein without its characterictic prosthetic group or metal
apoenzyme
the protein part of an enzyme without the cofactor necessary for catalysis (the
apoenzyme is the inactive enzyme which can form the active enzyme by binding of a
cofactor)
holoenzyme
the complete apoenzyme-cofactor complex that gives full catalytic activity
metalloenzyme
an enzyme that, in the active state, contains one or more metal ions which are essential
for its biological function
multienzyme
a protein processing more than one catalytic function contributed by distinct parts of a
polypeptide chain (domains), or by distinct subunits, or both
isoenzyme (isozyme)
one of a group of related enzymes determined by different genes and catalyzing the
same reaction; they have different physical, chemical and immunological properties
resulting from different molecular structures
isoform
one of a group of related enzymes determined by the same gene and catalyzing the
same reaction but their molecules differ by posttranslational modification (they are
„pseudoisoenzymes“)
proenzyme (zymogen)
an inactive enzyme precursor (e.g. pepsinogen, trypsinogen, proelastase)
allostery
a phenomenon whereby the conformation of an enzyme or other protein is altered by
combination, at a site other than the substrate-binding site, with a small molecule
(effector), which results in either increased or decreased activity by the enzyme
allosteric enzymes
enzymes which contain regions to which small, regulatory molecules (effectors) may
bind in addition to and separate from substrate binding sites; on binding the effector, the
catalytic activity ot the enzyme towards the substrate may be enhanced, in which case
the effector is an activator, or reduced, in which case it is an inhibitor
The allosteric enzymes exist in two structurally distinct forms, one of which is active and
the other inactive.
enzyme activity
cytalytical activity of an enzyme; it describes how many moles of substrate are
converted to products per unit of time (unit: katal; 1 kat = 1 mol . s-1)
concentration of catalytic
activity
it is used as an expression of the concentration of an enzyme in a biological material,
e.g. blood (unit: kat / L)
Michaelis constant (Km)
the concentration of substrate at which the rate of reaction is equal to one half of the
limiting rate (maximum rate); it is the constant of a pair enzyme-substrate and gives an
information about the afinity of the enzyme to the substrate: if the Km is low the afinity is
high and the other way round
effector
a small molecule which increases (activator) or decreases (inhibitor) the activity of an
(allosteric) protein by binding to the protein at the regulatory site (which is different from
the substrate-binding catalytic site)
enzyme activator
a substance, other than the catalyst or one of the substrates, that increases the rate of
a catalysed reaction without itself being consumed; the process is called activation
enzyme inhibitor
a substance that diminishes the rate of a chemical reaction; the process is called
inhibition; the inhibitor acts by binding to the enzyme

competitive
inhibitor
an inhibitor molecule that resemble the substrate and bind to the active site of the
enzyme, so preventing normal enzymatic activity; competitive inhibition can be reversed
by increasing the concentration of the substrate

noncompetitive
inhibitor
an inhibitor that binds to a part of the enzyme or enzyme-substrate complex other than
the active site, known as an allosteric site; this deforms the active site so that the
enzyme cannot catalyze the reaction; noncompetitive inhibition cannot be reversed by
increasing the concentration of the substrate
pH-optimum
pH at which the enzyme is the most active
temperature-optimum
temperature at which the enzyme is the most active
enzyme induction
the process whereby an (inducible) enzyme is synthesized in response to a specific
molecule (inducer) which combines with a repressor and thereby prevents the blocking
of an operator by the repressor
(= the process on the level of transcription)
inducer
often a substrate that needs the catalytic activity of the inducible enzyme for its
metabolism
enzyme repression
binding of a repressor to the operator sequence in an operon thus preventing the
transcription of the following structural gene(s) into mRNA and consequently synthesis
of enzyme (= protein)
the mode by which the synthesis of an enzyme is prevented by repressor molecules; in
many cases, the end product of a synthesis chain (metabolic pathway) acts as a feedback correpressor by combining with an intracellular aporepressor protein, so that this
complex is able to block the function of an operator, and the expression of all enzymes
necessary for the synthesis of the end product is abolished