1. Membrane physiology 2. Membrane models 3. Liposomes 4. Monolayers 5. SUV, MUV. LUV 6. bLACK LIPID MEMBRANE 7. MICELLES AND Bicelles

1. Model Membrane
Systems
By Ekeh Chukwuemeka Obinna
Department of Biochemistry
Sofia University St Kliment Ohridski

2. ● Singer and Nicolson Model(1972): Membranes are fluid and diffuse
laterally in the lipid bilayer. They propose two classes of membrane
protein( integral and peripheral proteins).
● Membrane fluidity modulated by cholesterol, nature of phospholipids,
temperature, temperature, hydration.
Fluid mosaic membrane model

3. Laboratory Membrane Models
● Liposomes:and
sonicated vesicles
● Classification of liposomes:
Nature of packing of the acyl
chain, size of aqueous space,
size, number of membrane layers
.
● Liposomes are created when
phospholipid is treated with
chloroform to form aggregate
which are dried on a film, hydrated
with a buffer and vortex until milky
suspension is formed.

4. Liposomes and sonicated vesicles
● They are used in study of cholesterol in mixture of lipids, membrane protein function, folding of
bilayer, proteins of interest reconstituted into the membrane.
● MLV have been used to study the lipid phase transitions, enzymes, peptide bond formation and
solute uptake rates.
● Solute uptake study: MLV + hypotonic
solution = uptake of water, swelling,
reduction of optical density.
● Incorporation of LamB protein
(maltoporin) increases the absorption
of maltose into the cell as against
when it is absent.

5. ● SLV: They are in small shape, reduced radius of curvature, less tightly packed
acyl chain, difficult to incorporate protein and difficult for membrane transport
study.
● SLV are used for peptide binding study. The heats of reaction for binding cyclic
peptides are exothermic, entropy is not useful in SUV binding but required for
LUV peptide binding.
● LUV: They have large diameter and more tightly bound acyl chain. They are
used to study the transport of substances cross membrane. Protein, lactose
permease and cytochrome o are inserted in the membrane while transport of
lactose is studied.

6. ● They can be loaded with pharmaceutical
products, gene, diagnostic agents
● Targeted to a specific tissue by attaching
a ligand on its surface.
● Administered via oral or parenteral
routes
● Proposal for use in cancer therapy
● They do not provoke toxic or
immunologic reaction.

7. Black lipid membrane
● It allows electrodes to be placed on both sides of a phospholipid bilayer for electrical conductivity
measurements. This system is commonly referred to as the black lipid membrane. Black lipid
membrane because of the optical behavior of the membrane when formed.
● Membrane becomes opaque due to destructive interference of reflected light from the front and
back of the film.

8. ● To investigate the hemolytic pore formation on
membranes by saponin(digitonin).
Conductance and fluorescence methods are
put into analysis.
● Result: Increase in conductance stimulates
reduction in NBD-Cholesterol complex
determine by fluorescent microscopy.
● Conclusion: Saponin doesn't require cholesterol
for insertion but required for pore formation.
● The formation of black membrane by
displacement of monolayers in close
proximity

9. ● Method: Excision of a part of the
membrane to form a seal and
remove closes the seal
● Conductance are carried out and
measured while the excision is
done.
● Patch clamp model.
● Supported membrane model (glass,
quartz, gold) allows for
immunolabeling,spectroscopy,
fluorescence.
● The support can be used as
biosensors for cell population and
ligand.

10. Monolayers
● To determine the surface area and
surface pressure.
● Surface pressure = Yo - Y
● To study phase changes of
membranes
● Relationship between surface
pressure and area of the
monolayer.

11. Monolayers
● When monolayers are made of phosphatidylcholine with
saturated acyl chains of varying lengths (, dibehenoyl [C22]; o,
distearoyl [C18]; x, dipalmitoyl [C16]; ∆, dimyristoyl [C14]; and
∇, dicapryloyl [C10]) phospholipid behavior in the monolayers
correlates with their melting temperatures
● The longer chains and higher melting temperatures form
liquid condensed (LC) monolayers at 22°C, while the PLs with
shorter chains and lower melting temperatures form liquid
extended (LE) monolayers at 22°C.
● To study effects of lipid factors such as PH, Ionic strength and addition of monovalent ions.
● They are use to study the respiratory distress syndrome in the newborn.
● Monolayers can determine the conformation of signal peptides as they interact with
membrane lipids.

12. Nanodiscs
● To study the mechanism of testosterone metabolism. CYP3A4, a cytochrome P450 that is involved in
steroid biosynthesis in humans, cycles through seven intermediate states during catalysis. Membrane
cytochrome p450 Incorporated into nanodiscs, CYP3A4 monomers cooperatively bind three
molecules of testosterone, exciting a shift in the ferric spin state equilibrium previously the binding is
difficult to achieve due to aggregation but nanodisk facilitates this binding. Biophysical studies like
spectral titration of the intermediates, kinetics of NADPH consumption, and kinetics of product
formation

13. Micelles
● Micelles is the structural rearrangement of phospholipid
molecules into spherical shape in aqueous solution or
detergents. It usually occur in a well hydrated polar head.
● When water is in contact with the lipid bilayer. It rearrange to
trap water between the polar head.

14. Bicelles
● Bicelles are the bilayer micelles rearrangement which
closely imitate the lipid bilayer and avoiding extreme
membrane curvature.
● Figure A contains low concentration of bile salt
DETERGENT while figure B contains long chain
phospholipid,at the base short chain lipids and
proteins incorporated
● They are used for study involving solid state nuclear
magnetic resonance.

15. ● Bicelles can be used in skin research.
● They can modify the biophysical parameters and
modulate skin barrier function.
● They are used as carriers for incorporation of
different molecules through skin layers