Substrate analogs (substrate state analogues), are
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
s with a
chemical structure
A chemical structure determination includes a chemist's specifying the molecular geometry and, when feasible and necessary, the electronic structure of the target molecule or other solid. Molecular geometry refers to the spatial arrangement of at ...
that resemble the
substrate molecule in an
enzyme-catalyzed chemical reaction
A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
. Substrate analogs can act as
competitive inhibitors of an enzymatic reaction. An example is
phosphoramidate
Phosphoramidates (sometimes also called amidophosphates) are a class of phosphorus compounds structurally related to phosphates (or organophosphates) via the substitution of an OR for a NR2. They are derivatives of phosphoramidic acids O=P(OH)(NR2 ...
to the ''
Tetrahymena
''Tetrahymena'', a Unicellular organism, unicellular eukaryote, is a genus of free-living ciliates. The genus Tetrahymena is the most widely studied member of its phylum. It can produce, store and react with different types of hormones. Tetrah ...
'' group I ribozyme Other examples of substrate analogs include 5’-adenylyl-imidodiphosphate, a substrate analog of
ATP, and 3-acetylpyridine adenine dinucleotide, a substrate analog of
NADH
Nicotinamide adenine dinucleotide (NAD) is a coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an aden ...
.
As a competitive inhibitor, substrate analogs occupy the same binding site as its analog, and decrease the intended substrate’s efficiency. The maximum rate (V
max) remains the same while the intended substrate’s affinity (measured by the Michaelis constant K
M) is decreased. This means that less of the intended substrate will bind to the enzyme, resulting in less product being formed. In addition, the substrate analog may also be missing chemical components that allow the enzyme to go through with its reaction. This also causes the amount of product created to decrease.
Substrate analogs usually bind to the binding site reversibly. This means that the binding of the substrate analog to the enzyme’s binding site is non-permanent. The effect of the substrate analog can be nullified by increasing the concentration of the originally intended substrate. There are also substrate analogs that bind to the binding site of an enzyme irreversibly. If this is the case, the substrate analog is called an inhibitory substrate analog, a suicide substrate, or a Trojan horse substrate. An example of a substrate analog that is also a suicide substrate/Trojan horse substrate is
penicillin
Penicillins (P, PCN or PEN) are a group of β-lactam antibiotics originally obtained from ''Penicillium'' moulds, principally '' P. chrysogenum'' and '' P. rubens''. Most penicillins in clinical use are synthesised by P. chrysogenum using ...
, which is an inhibitory substrate analog of
peptidoglycan
Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like peptidoglycan layer outside the plasma membrane, the rigid cell wall (murein sacculus) characteristic of most ...
.
Some substrate analogs can still allow the enzyme to synthesize a product despite the enzyme’s inability to metabolize the substrate analog. These substrate analogs are known as gratuitous inducers. An example of a substrate analog that is also a gratuitous inducer is
IPTG (isopropyl β-D-1-thiogalactopyranoside), a substrate analog and gratuitous inducer of
β-galactosidase
β-Galactosidase (EC 3.2.1.23, lactase, beta-gal or β-gal; systematic name β-D-galactoside galactohydrolase), is a glycoside hydrolase enzyme that catalyst, catalyzes hydrolysis of terminal non-reducing β-D-galactose residues in β-D-galactosi ...
activity.
[Garrett, Reginald H.; Grisham, Charles M. (2013). Biochemistry (5th ed. ed.). Belmont, CA: Brooks/Cole, Cengage Learning. p. 108. ]
See also
*
Enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
*
Enzyme inhibitor
An enzyme inhibitor is a molecule that binds to an enzyme and blocks its activity. Enzymes are proteins that speed up chemical reactions necessary for life, in which substrate molecules are converted into products. An enzyme facilitates a sp ...
*
Suicide inhibitor
*
Structural analog
A structural analog (analogue in modern traditional English; Commonwealth English), also known as a chemical analog or simply an analog, is a compound having a structure similar to that of another compound, but differing from it in respect to a ce ...
, compounds with similar chemical structure
References
{{Reflist
Enzyme kinetics
Chemical nomenclature