Mechanism of action of ionophores, examples and their significance in a cell

1. BY:
MANIRIHO HILLARY
MSc.BIOCHEMISTRY(UOM)

2. contents
 Etymology and definition
 Classification of ionophores
 Mechanism of action
 Examples of ionophores
 Applications of ionophores
( importance)

3. IONOPHORES
Etymology
ιόν = ion (Greek)
Φέρω( phero) = carry ( Greek)
 ionophores can be literally called as “Charge
carriers / charge bearers” .
The word ionophore was coined by Pressman in
1964. Ionophores, initially called ion complexers
were discovered in 1950’s and first used as anti-
coccidial agents.

4. • Ionophores are specific molecules that
complex /carry specific cations and
facilitate their transport through
biological membranes.
• They are molecules that act as
membrane shuttles for particular ions
across the lipid membranes with out
expenditure of energy

5.  Ionophores contain hydrophilic centres that
bind specific ion(s), and a hydrophobic
portion that interacts with the lipid interior
of the membrane
 Most ionophores adopt a cyclic ring
formation by concentrating oxygen/ nitrogen
functional groups at the centre of their
structure to associate with the cations.
 With the hydrophobic groups in contact
with the acyl groups of the membrane , the
ionophore is able to “ dissolve” and diffuse
to the opposite side of the membrane

6. Classification
 ionophores can be classified based on;
Mechanism of their
action
Chemical structure

7. Based on the mechanism of action
a) Mobile carrier ionophores :
These bind to a particular ion and shield its charge
from the hydrophobic environment of the
membrane . They form a lipid soluble complex with
the cation which then diffuses across the
membrane. Eg Valinomycin – K+
By reversibly binding to the ion to form lipid soluble
complexes which rapidly diffuse across the
membrane, they catalyse passive transfer of cations
across the otherwise impermeable hydrophobic
membrane.

8. Generally;
 three steps are involved ;
Complexation of the ionophore with
the ion
Diffusion of the complex via the
membrane interface to the other side
of the membrane.
Reverse complexation process

9. illustration ion
ionophore

10. (b) Channel- forming ionophores
 These introduce a hydrophilic pore
into the membrane allowing specific
cations to pass through with out
coming into contact with the
hydrophobic interior of the
membrane ,eg Gramicidin. Channel
forming ionophores are usually large
molecules

11. Channel of the
ionophore
ion

12. Based on the chemical structure;
i. polyether ionophores eg monensin and maduracin
ii. Peptide ionophores
iii. Cyclodepsipeptide ionophores eg Valinomycin
iv. Macrotetrolides ( macrocyclic compounds
containing tetrahydrofuranyl carboxylic acid
residues linked together)
v. Cryptates ( synthetic bi and polycyclic
multidentate ligands for variety cations)
vi. Crown ethers eg

13. a crown ether
cation
associate
region

14. Example of Ionophores

The biologically
significant classes of
ionophores are the channel
forming and the mobile
carrier ionophores;

15. 1. Valinomycin
These is a circular depsipeptide molecule which
contains ester and amide linkages ( A depsipeptide is
a molecule containing both peptide and ester bonds ).
It contains D- valine, L- valine, L- Lactic acid and
hydroxyisovaleric acid.
 Valinomycin is specific to K+
ions, which it transfers
in complexed and uncomplexed state. It has a
pluckered ring , stabilized by hydrogen bonds which
therefore suits it to surround single un hydrated K+
ions

16. representation
Valinomycin
O
O O
O O
Hydrophobic
O
K
+

17. Chemical structure

18. How it works,
The six oxygen atoms of the ionophore interract with
the bound K+
ion replacing the O-atoms of water of
hydration.
Each valinomycin molecule is able to carry about
10000 K+
ions per second – Very rapid transport rate!
NB. Valinomycin can not carry sodium ions because
they are small and there fore can not simultaneously
interact with six O-atoms – thus being energetically
unfavourable

19. 2. Gramicidin A
 This is a linear 15-amino acid -peptide with
alternating D- and L- amino acids . The structure is
double helical in organic solvents and is an end-to-
end dimer in water.
 In lipid bilayer membrane, gramicidin dimerises and
folds as a right hand β-helix. The dimer spans the
bilayer . The hydrophobic outer surface of gramicidin
dimer interacts with the core of the lipid bilayer
while the ions pass through the more polar lumen of
the helix.

20. cont;
 Gating (opening and closure ) of gramicidin channels
is thought to involve reversible dimerisations . An
open ion channel forms when gramicidin molecules
join end to end to span the membrane .
Cations there fore move through the channel in a
single file along with a single file of water molecules.

21. linear structure

22. Folding of gramicidin

23. model of gramicidin
Channel for the passage of ions
Carbon atom
Nitrogen atom
Oxygen atom

24. 3. Ionomycin
 Has a hydrophobic periphery.
It carries Ca2+
ions into the cells and organelles.
 It was first isolated from bacterium Streptomyces
conglobatus. Calcimycin (ionophore A23187) is also a
calcium ionophore that was first isolated from the
fermentation reactions of Streptomyces chartreuses.

25. chemical structures
ionomycin calcimycin ( ionophore –A23187)

26. 4. Monensin
It was first isolated from Streptomyces cinnamonensis
It complexes with Na+
and H+
ions . It is a polyether
anti-biotic.

27. Siderophores
These are bacterial ionophores specific for carriage of
Fe3+
ions . Complexation of Fe3+
ions solubises it for its
uptake . The binding ligands are catechols
( orthohydroxyphenol).

28. 6. Nigericin- exchanges H+
and
K+
ions across the membrane

29. 3,5-dinitrophenol (DNP)
It is a hydrogen ion ionophore and a chemical
uncoupler. It rapidly transports protons from the
cytosolic side to the matrix side of the inner
mitochondrial membrane
H
H+
High hydrogen
ions on the
cytosolic side
causes DNP to
be protonated
-
Low hydrogen ion
concentration in the matrix
causes DNP to dissociate
releasing protons
Inner mitochondrial
membrane
DNP
Carbonylcyanide –m-
chlorophenylhydrazone (CCP)
also acts in similar way leading to
non-voltage dependent proton
transfer

30. 7. Beauvericin
Beauvericin is a cyclic hexadepsipeptide with alternating methyl-
phenylalanyl and hydroxy-iso-valeryl residues. Its ion complexing
capability allows beauvericin to transport alkaline earth metal and alkali-
metal ions across cell membranes.
Region where a
cation is bound(
polar region of
the molecule)

31. 8. Enniatins
 These are mixture of depsipeptides that bind and
transfer ammonium ion across the membrane

32. other ionophores;
salinomycin,
lasolacid,
octadecadienic acid (first isolated in the
mitochondria of the beef heart)
and many others…

33. Importance of ionophores
They creat electrochemical gradient resulting in
changes in the physiological state of the cell such as;
Oxidative phosphorylation,
Osmotic balance ,
Neurotransmission,
Cell signalling.
Hormone Action etc.

34. exploiting the effects of
ionophores……….
As antibiotics and treatment of
coccidiosis in poultry.
 Coccidia parasites do not have
osmoregulatory organelles . Treatment with
ionophores therefore disrupt the osmotic
balance resulting in the influx of water and
subsequent vacuolarisation of the cell
resulting in bursting of the cell.

35. effects on bacteria……..
 In bacteria , ionophores disrupts the electrochemical
gradient there by causing cell death particularly in
gram-positive bacteria.
This is because, they are surrounded by
peptidoglycan layer which is porous and therefore
allow the lipophilic ionophores to pass through.
However , gram –negative bacterial cells are
surrounded by a lipopolysaccharide layer which does
not allow the ionophore to pass through thus they
are passive to ionophores.

36. Feed additives in live stock
Ionophores are used in therapeutic levels to improve
the feed efficiency in livestock.
Ionophores target ruminant microbial population
thus altering their ecology.
This subsequently results into carbon and nitrogen
nutrient retention by the animal
Example

37. case example of monensin…
 Monensin is used as a methane inhibitor and a
propionate enhancer ( more efficiently utilised)
ruminants. It also reduces dietary protein
deamination resulting in less ammonia in urinary
excretion. This increases energy availability and
nitrogen retention thus improving animal
productivity.
 By reducing the population of fermenting bacteria
(methanogens) , monensin reduces methane
production by 30% and amino acid degradation by
50% . However, error in administering may result in
toxicity, to the animal neuropathy and muscle

38. biomedical science Research
 Many ionophore have been utilized in manipulating
the physiological state of the cell during research.
example;
 Monensin action disrupts the Golgi functioning .
Calcium and ionomycin are used to introduce calcium
in the cells and organelles. Many physiological
processes that are normally triggered by the binding
of hormones to cell surface receptors can be elicited
by use of calcium ionophores to raise cytosolic
calcium level.

39. Cont;
Enniatin inhibits acyl-COA cholesterol transferase
Valinomycin. Inhibits phytohemagglutin
(PHA)stimulated blastogenesis and proliferation in
human lymphocytes.
Gramicidin A and nigericin exchange H+
and K+
across the mitochondrial membrane and uncouples
oxidative phosphorylation. They combine with K+
ions
and transfer it to the cytoplasm where they are
protonated as they diffuse to the outer membrane
surface . This induces non-voltage dependent H+/
K+
exchange in the mitochondria

40. cont;
DNP and CCP are chemical uncouplers . Uncoupling
results into non- shivering thermogenesis.
Many ionophores have also been used to make the
membrane selective electrodes in electrochemistry

41. Conclusion
 Ionophores are molecules that are able to shuttle
ions across the otherwise hydrophobic lipid layer of
the cell membranes
 The major two classes of ionophores ( channel
forming and mobile career ) particularly Ionomycin /
calcimycin and valinomycin ;
Are applied to increase calcium levels in
pharmacological research
 Are used as antibiotics
Are used to design membrane selective electrodes

42. Thank you