Biochimica a Biophysica A~a 860 (198~ 286-292
~
286
BBA 73246
Interaction ~ l~t~n wi~ phosphatidykhofine bilayets
V.K. C h ~ u ~ e ~ and C.K. Ramakfishna Kurup *
D~a~m~t ~ ~ o c h ~
In.an ~
(R~d
~ ~ en c~ B ~
560012 H n ~
M ~ c h 1 8 ~ 198~
Key words: Lutein; Phosphofipid membrane; Phase ~an~fion; ESR; Differenti~ scanning calorimetry; NMR
The interaction of l u t ~ an ~ b ~ o r y uncou~er of m~ochondfi~ ox~ative phosphory~tio~ with phospholi~d bilaye~ has been examined e m ~ o y ~ g a varieW of phy~c~ method~ Dffferenti~ c~o~metric scans
reve~ed that incorporation of lute~ ~to aqueous ~sper~ons of dip~mitoylphosphatidylch~ine broadened
the m~n ~ansition endotherm and decreased the ~an~fion enth~py as well as the ~ze of the cooperative
u~t without change ~ the ~mperature of ~an~tion. Permeabili~ of the bilayer ~o ascorb~e was enhanced
~gnff~antly by the presence of lutein. The ~apped v~ume of the veeries was decreased. Incorporation of
hitein broadened the NMR peaks of both the ac~ ~d~ch~n meth~ene and ~rmin~ m ~ h ~ protons without
any change ~ the ~ne-width of the choline head-group m~hyl proton ~gn~. Th~ ~ c M e d the abiliff of the
compound to integrate deep hito the hydrophobic re~ons of the phospholipid bilayer ~ s t ~ to the polar
re~on~ The~e r e s ~ suppo~ our earlier ~ o c h e m ~ stu~es wh~h reve~ed thM the dde~fious action ef
~ t ~ n on m~ochondfi~ o~dative phosphorylation co~d be due to ~s abiliW to ~ r a ~ with membrane
componen~ and perturb the structure.
In~ucti~
There ~ increasing e~dence that interaction
between the two energy-~ansdudng organelles of
higher phn~, namdy the chloroplast and the
mitochondrion, plays an impo~ant role in the
regulation of energy metabohsm [1-5]. In confo~
mity with this, we reported recently that chloroplasts uncoup~ mitochondti~ oxidative phosphorylation [6]. A factor with uncouphng and
inhibitory actions on oxidative phosphorylation
was purified from chloroplas~ and identified as
the xanthophyll luton [7]. Luton ~ a lipophile
containing two hydroxylated asymmetric fl-ionone
* To whom ¢o~espondenee shoed be addre~ed.
Abb~fiafions: DPPC, 1,2-dip~mi~yl-3-sn-phosphatidylch~
~ne; ~ S A S ~ N-oxyl-4',4'-~methyloxazofidine derivative of
5-k~os~aric a~d; TEMPO, 2 ~ , ~ a m e ~ y ~ e r i ~ n ~ N oxyl; t ~ , h~f-li~; MLV, m d ~ a m d l ~ vefid~; n, coope~
ative u~t; T~, ~ m p ~ u ~ of p h a ~ ~anfifion.
tings bridged by a long chNn of four isoprene
units [81.
Purified preparations of the factor showed a
~ndency to bind firmly to mitochondria and to
induce swdhng. It stimulated the dormant ATPase
of tightly coupled mitochondria for which the
presence of Mg 2+ in the reaction sys~ms was
obligatory [6,7]. These properties suggested that
disruption of membrane organization may hold
the key to the mode of action of the compoun&
This aspect meri~d deeper ~udy. The mitochondfi~ membrane which is composed of a great
varify of protons and hpids is too comp~x to be
amenable to exploratory ~ u d ~ Therefore, as a
first ~ep, we have op~d for the fimpler modal of
dip~mitoylphosphatid~chohne (DPPC) verities
for ~eaning bafic information on the infraction
of the factor with bihyers of membranes. For the
study, DPPC was chosen because it is the most
used and best-characterized veficular sys~m [9].
Moreove~ phosphatid~chohne is the predominant
0005-2736/86/$0330 © 1986 Else~er S~ence Publishers B.V. (BiomedicM Diction)
287
hpid in the mitochondfiM membran~
It is wall-recognized that the phase state of
component fipids plays a m~or role in lhe control
of membran~mediated functions [10]. The influence of lutdn on the themrotrop~ phase behaviour of aqueous disperfions of DPPC was investigated by differentiM scanning cMofime~y and
dec~on spin resonance. Proton-NMR was used to
visualize the infraction of luton with acyl fidec h i n s. ARerations in the permeabi~ty profile of
the verities were Mso monitored. The data presented in this paper reveM that the compound
penetrates deep into the hydrophobic dom~ns of
the b~aye~ disrupting cooperative interactions
among the acyl fid~ch~ns of phospholipids and
increafing permeability.
M~efifls and M~hods
~
The ~ o ~ h ~ d
( D P P Q was purchased from
~gma C ~ c M
Co., St. Lo~s, MO, U.S.A., and
the ~
la~ds ~ E M P O and 5-SASL) ~om S ~ a
Rehash C~c~,
U.~A. The uncoupl~g factor ( ~ n ) was ~ e d
~ pure ~ r m ~om M ~ f a
( ~ ~
saava) c ~ o ~
as described e a ~ e r
[7]. The puri~ w ~ confirmed by h i g ~ p ~
mance fiq~d chrom~ography. In ~ew of its unstab~ nature, fresh preparations of the compound
were used ~ r experimems as far as posfib~. ~ 1
other ~ e ~ c ~
used wefe of the purest grade
~ .
S ~ m ~ n s were prepared ~ water doub ~ - ~ s ~ d ~ an Ml-quar~ app~ a ~ s .
Memo&
Scann~g c a ~ m ~ .
M d ~ a m d h r verities of
DPPC were prepared by ~ e r s i n g 15 mg of the
lipid ~ a t ~ n ~ m ~ 0.5 ml of double-distilled,
ddo~d
w~e~ D i ~ o n
w ~ achieved by a~tation on a vo~ex m~er ~ r a ~w minutes a ~
heating to 50-55°C [11]. I n c o r p o r ~ n of ~ t d n
into the veeries was achieved by ad~ng a s~ution
in c ~ o r o ~ r m at the time of ~ r m ~ n of ~ e fip~
thin ~m.
Th~mograms w~e obt~ned u~ng a P ~ m
~ m ~ DSCQ0 ~ a n ~ n g cM0fime~r ~ a ~ a n ~ n g
speed of 2.5 Cdeg/min and a ~ n ~ t i f i f f of 1
m c M / ~ The ~ m p ~ of MLV (10 ~D w ~ h~metically seMed ~ an Mumi~um sarape pan. I n , u r n
and cydohexane were used as standards for
calibration. Change in enthMpy (AH) was cMculated from the area of the Uanfition curves. An
approxima~ ~ze of the cooperative unit (n) was
cMculated ~om the equation
n
6.9~
(a~
× an)
where Tm is the ~anfition ~mperatur~ ATml/2
the tianfition width at hM~hdght and AH the
~anfition enthMpy [12-1~. AnMyfis of the samples by thin-layer chromatography confirmed that
no decompofition of the phospholipid or the
xanthoph~l had taken place during the runs.
Nuclear m a g n ~ resonance. From MLV d~pe~
sed in H20 , unilamellar verities were prepared by
sonic di~uption with a Branson B-12 sonifier fit~d
with a microtip (25 min, power output 60%; ternp e r j u r e 45°C). The s~ghfly turbid sonicate was
centrifuged in a Beckman L5-50 ul~acentrifuge at
100000 × g for 30 min to remove any multilamdlar structures present [15]. A vefic~ar diame~r of
26 nm was obt~ned by the hnthanide shi~ reagent method [16,17]. That sonic di~upfion had
not produced~ny chemicM degradation was confirmed by thin-layer chromatography [18].
Proton NMR spe~ra were recorded on a Bruker
WH-270 spec~ome~r operating at 50°C in the
Fourier ~an~orm mode at 270 MHz. Field
~equency lock was prodded by the deuterium
fignM of s o l v e n t 2H20.
E ~ r o n spin resonance. Vesicles were prepared
in 10 mM phospha~ buffe~ pH 7.4. The spin
labd was incorporated at a molar ratio of 100
(lipid):1 (probO and 50:1 for TEMPO and 5SASL, respectively. S p e ~ a were recorded in an
X-band ESR spec~om~er with a Varian 12 inch
magn~ and a ~ o o a ~ d fidd dim and a VFR 2501
power supp~ coupled to a Vafian V-45601, 100
kHz fidd modulation and d~ection unit. Temperatures were con~olled to ± 1 Cdeg by a Varian
V-4540 regulato~
Phase ~anfition was monitored by the ~m pe~
atur~dependent changes in TEMPO partition in
the MLV bflayer as ~ven by the param~er ' f '
which was cMcula~d as
f
H
H+P
288
where H and P were the hdghts of the high-field
fignal in ~pid and aqueous phase, respectivdy
[19,20]. The permeability of unilamdlar veficles to
ascorbate was assessed by monitoring the kinetics
of decay of the ESR fignal of 5-SASL on addition
of 20 mM ascorbate at 45 oC.
Trapped volum~ Veeries were made in 0.1 M
acetate buffeL pH 5.~ in the presence of 0.5 M
K3Fe(CN)6. After incubation at 45°C for 3 h, the
preparation was fiRered through a Sephadex G-50
column (1 × 28 cm) u~ng the buffeL Fractions
containing the veeries were pooled and the
trapped K3Fe(CN)6 was rdeased by the addition
of n-propanol (40% v / v ) and estimated by absorbance at 420 nm [21]. Absorbance was recorded with a Shimadzu UV-200S spectrophotometer. The concentration of hpid was estimated
by the phosphorus method [22]. A high concentration of ferficyanide was used to eliminate any
error due to binding to the phospholipid [23]. In
all experiments, incorporation of lut~n into the
hposomes was monitored by g d fil~ation and
chromatograph~
Resd~
ScannMg c a ~ m ~ r y
CMorimetric heating scans of DPPC veeries
containing increasing concen~ations of luton are
depicted in Fig. 1. In the absence of lutein, the
thermogram is characterized by a sharp peak at
41.5°C, signifying the gd to liquid-crystalline
phase ~anMfion of the phospholipid, and a pre~an~tion peak at 3&5°C [24]. The enthMpy
change (8.66 kcM/mol) and the half-h~ght width
(0.4 Cdeg) Mso agree wall with the reposed vMues
[25]. Incorporation of lut~n causes the main endotherm to broaden and decrease in h~ght without
any ~gnificant change in the midpoint of the
~an~fion (Table I). Pre-~an~fion is abolished at
the lowest concentration of luton used.
The decrease in AH with increase in the molar
ratio of luton was finear and ex~apolation of the
regres~on fine (correlation coeffioent 0.998) indicated that the ~an~fion would be abofished ( A H
= 0) at 2 mol% of luton (data not shown). The
broadening of the endotherm indica~s that the
factor decreases the cooperativity of ~an~tion
~Z13~
The effect is qui~ ~gnificant, even the
L~n (m~e~
~ , . . . ~ 0.00
o
W
~
~
~
02
.6
052
07
.8
~
1.04
I
30
I
I
35
40
Temper~ure (°C)
I
45
Fi~ 1. Ef~ct of Mcorporm~n of ~tein on ~e ~ermo~op~
tranfit~n of m ~ a m d ~ r vefid~ of DPPC. DifferendM
cMofim~fic scans of DPPC mM~ayers in excess water wi~
increasing concen~ations of ~tein are showm For each scan
400 nm~ DPPC w~e use& Other d~Mls a~ Dven ~ Ma~fiMs
and M~hod~
~west concentration s h r i n i n g the fize of the cooperative unit to o n ~ t h i ~ (Table I).
E~ctron spin resonance
A plot of the T E M P O partition parameter ' f '
as a function of temperature (Fig. 2) shows that
the incorporation of lut~n into MLV changes the
ampfitude of phase ~an~tion without change in
Tm (41°C). This is in close agreement with the
resul~ obtained in calorimetry.
The effect of the factor on the permeabihty of
unilamellar ve~cles to ascorbate as monitored by
289
TABLE I
E F F E C T O F I N C O R P O R A T I O N OF L U T ~ I N ON T H E T H E R M O T R O P I C T R A N S I T I O N O F M U L T I L A M E L L A R V E ~ C L E S
O F DPPC
The ~ m p ~ a m m s ~ pr~transition, m ~ n ~anfition (Tin) and full w i d ~ ~ h ~ f m a f i m u m ~ m ~ n transition ( T m ~ ) ~ e ~ n .
fize of h e cooperative u ~ t ( n ) and e n t h ~ p y change ( A H ) were c M c d ~ e d as described ~ the text.
Lutein
(m~%)
P~anfition
(°C)
M ~ n ~anfition
Tm
(°C)
Tm~~
(°C)
E n ~ p y change
AH
~cal/mol)
Cooper~ive
umt
(n)
0.~
0.26
0.52
0.78
1.04
3<5
-
41.5
41.5
41.0
41.0
41.0
~4
1.5
1.9
2.3
3.0
8.66
7.33
5.97
4.88
4.03
197
62
60
60
56
--
The
__
the ~nedcs of reduction of the b~ayevembedded
5-SASL is presented in Fig. 3. As expected, the
reduction fo~ows a biphasic pattern, the initial
faster and the subsequent slower phases corresponding to the rate of diffufion of ascorbate into
the outer and inner monolayers, respectively
[27,28]. Incb~oration of lutein increases the rate
of reduction in both layers. ~ s is clearly shown
!
I
I
04~
~
!
~
I
_
~.o
_
•
~
--
I
~ n ~
36
I
I
_
•
~2
'
-
02--
-2
~
~
~
4
~
--
~
~
o
~
I
20
I
40
30
~mD~e
I~
20
Time (rain)
50
(*C)
~
2. E f f ~ t of ~ c o ~ a t i o n
of ~ t ~ n on the p ~ f i t ~ n of
T E M P O M ~ multilamell~ veMdes of DPPC. The order
pa~m~s
~ ' c M c ~ a ~ d ~ o m ESR fignM h o g h ~ ~ T E M P O
inco~ated
~
multilamell~ ~ f i c l e s ~ DPPC ~ the ab~ n ~ (~) and p ~ n ~
~ ~ 4 4 m ~ % ~ ~ t e i n ( © ) am ~ n
~
a ~ r orion ~ ~ m p ~
O~
detMls ~ e # ~ n M M~efiMs
and M ~ h o d ~
~
3. Effect of ~corporation of ~ t ~ n on the p ~ m e a ~ f i ~ of
DPPC bilay~s to ascorbate. PermeaMfi~ was m o ~ d
by
h e decrea~ ~ ESR fignM of 5-SASL cn ~d~tion of 20 m M
a s c o r b a ~ ~ u ~ M m e l l ~ v e f i d ~ of DPPC. The M g a f i ~ m of
~gnM h o g h t ~ # o t t e d as a function of time for DPPC Mone
( © ) and ~ r DPPC c o n t M ~ n g 0.44 m ~ % of ~ t e i n (~). The
m e a s u ~ m e n ~ w e ~ carried out ~ 45°C. The ~ g ~ n
lin~
fit~d by h e Ma~-squares method are d r a w ~
290
TABLE II
TABLE III
EFFECT OF INCORPORATION OF LUTEIN ON THE
HALF-LIFE OF R E D U C T I O N OF 5-SASL BY ASCORBATE
EFFECT OF INCORPORATION OF LUTEIN ON THE
TRAPPED VOLUME OF UNILAMELLAR VESICLES OF
DPPC
H ~ f life ( q / ~ ) of reduction of ~ S A S L was c ~ c d ~ e d from
~ g ~ s ~ o n ~ u a t i o ~ by ~ e ~ r m ~ a q ~ = ~ 6 ~ / K where K
is ~ e s ~ p e ~ l i n ~ depicted ~ ~ g 3. The v~ues of co.clarion
coeffiden~ ( r ) ~ r ~ o n
a~ ~so ~ve~
Mea~men~
w ~ e made u~ng KaF~CN)6. D ~
in the M ~ e f i ~ s and M e ~ o ~ section.
Lu~in
(mol%)
Trapped volume
(h~e/m~)
Lutein
(mol%)
0~0
0.25
0.50
0.75
0.44
0.20
0.15
0.15
0
r
t~/~
t~/2
0.44
(min)
(rain)
r
Outer
bilayer
Inner
b~ayer
0.99
4.4
2.4
0.97
0.97
16.6
4.5
0.93
by the ta/z of reduction calculated from regression
equations (Table II). In lutein-incorporated
verities, the tl/~ of reduction is decreased substantially in both layers of the b~ayers, indicating a
significant increase in the permeability to ascorbate.
~IC
~
_
-N-~
o
o
~
~
I
O 25
O 50
I
075 inol -CH3
025
~
I
I¸5
0 50
~
0
~m
7
~D
Nuc&ar magnetic resonan~
The ~ g h ~ u f i o n
proton NMR ~ u m
of
s o , c a r d veeries of pure DPPC showed a strong
and sharp ~ g n ~ at 3.24 ppm [-N ~(CH3) 3 pm~n]
and peaks at 1.29 ppm [ ( C H 2 ) ; proton], 0.89
ppm [termin~ -CHa p r ~ o ~ and 4.56 ppm
(H~HO) as ~ p o ~ e d by Darke et ~. [29]. Incorp~
ration of lut~n produces broadening of b o ~ fatff
ac~ meSSene and termin~ m e ~ pro~ns (~g.
~ w i ~ o ~ any cbange in the fine width of the
c h ~ e ~gn~, ~ c ~ g
~ ~ e presence of htein
is sensed o ~ y by the hydrophob~ ~de chins in
• e fl~d state.
Trappedvolume
_
I
are Dven
5
Incorporation of lutein decreases the trapped
volume of unihmellar vesicles (Tab~ III). The
intern~ volume of pure DPPC verities agrees well
with the repor~d v~ues [30]. It may be mentioned
that the incorporation of lutein does not ~ter the
dution profile of the verities on fikrafion through
Sepharose 2B or sephadex G-25. Therefore the
decrease in ~apped volume does not indicate a
change in ~ze, but only the ~akage of trapped
ferricyanide from luton-incorpora~d vefide~
during ~olatiom
D~cus~on
~ g . 4. Effect of incorporation of ~ t o n on ~ e p r o ~ n N M R
spe~ra of DPPC bflayers. The ~ r m i n ~ -CH 3 and a c ~ h ~ n
-CH 2- spe~rM re~ons at varying concentrations of lutein are
showm Inset shows the percent increase in tin.width on
i n c o r p o r ~ n of lutom The spec~a were recorded at 5 0 ° C in
2HzO.
The thermotropic behaivour of aqueous dispe~
sions of DPPC on incorporation of lutdn reve~s
that the xanthophyH pe~urbs the bilayer. In
lowering A H and the ~ze of the cooperatNe unit,
291
the factor emulates cholesterol [31], cardioto~n
[26,32] and cenNn in~grM proteins of membranes
[33,3~. It has been reposed that ~eroids which
depre~ed and broadened the thermotropic phase
Uanfition of DPPC were locN~ed within the ac~
reNon of the bihyer and that ef~cts of the ~eroid
did not extend to the head-group or in~fface
reNons [35]. Our experimentN data indicate a
fimilar action for lutNn Nso. The decreases in
enthNpy and ~ze of the cooperative unit suggest
d~ruption of cooperative infractions among the
fatty ac~ chNn~
The infraction b~ween the packed ac~ chNns
of the bihyer and the xanthophyll seems ~oichiometric in ~ew cf the excellent co~dation b~ween
the decrease in ~ H and concentration of lutNm It
would appear that one molecule of the pigment
prevents 50 molecules of the phospholipid ~om
undergoing phase uanfition ( ~ H = 0 at 2 mol%
lutNn). This concenUation is considerab~ lower
than that of cytochrome b5 (7 mol%), cardioto~n
(10-20 mol%) or of cholesterol (33 tool%) required
for the abolition of phase ~anfition OL2L3~.
A shrinkage of the duper fize of the molecules
in the ~eNon ef phase Uanfition may ~ad to
generN di~uption of cooperative thermodynamic
finkages among the membrane components and to
M~rations in the kinetics of pasfive Uanspo~.
LocN di~uption of ac~ chNn packing without
s~nificant influence on bulk-phase chNn motion
may Mso be en~sage& The disappearance of pre~anfition at a relativdy low concen~ation of the
factor may reflect a Uan~ormation in the structure of the bihyer and the formation or elimination of 'ripples' [36]. It may be poin~d out that
the shape of the endotherm reveMs that incorpor~
tion of lutNn does not ~ad to phase separation.
Choles~rol, for example, splits lhe endotherm into
two at high concentrations [13].
The inference that lutein pe~urbs ac~ chNn
p~cking is supperted by the observed increase in
the permeability of the b~ayer to ascorbate and
the decrease in the concentration of trapped ~rricyanid~ The broadening of the meth~ene and
m ~ h ~ proton fignMs indicates that the factor
re~ficU thNr motionM ~eedom [37]. In other
word~ lutein in~gra~s deep into the hydrophobic
domNns of the bHayer di~N from the choline
head group of DPPC. This would faNfita~ the
di~uption of hydrophob~ and Van der WaM's
forces and loosening of fatty add c h i n packin~
The possibility that the increase in permeability
resul~ ~om the induction of 'aqueous poreg as
has been proposed to expl~n the action of polyene antibodies which ~so decrease trapped volume
[38] cannoL howeve~ be excluded. We have observed that Lutdn increases lhe permeabifity of
phospholipid verities and mitochondri~ membrane to Ca 2+ (unpubfished observationO.
It may be pertinent to mention in this context
that the effect of uncouple~ of o~dative pho~
phor~ation on the thermotropic properties of fipid
bilayers is qui~ different from that observed with
luton. Thus the dasficM uncoup~r 2,4-dini~ophenol lowered the ~mperature of the m~n
~anfition and split the endotherm [3~. It may
~so be mentioned that other lipophil~ compounds which cont~n an ~oprenoid c h i n Mso do
not produce the effects shown by lutein. Thus,
incorporation of ubiquinone (25 m~%) produces
very htfle change in the therm~ properties of
phosphofipids ~0~1]. The effe~s of luton in gener~ apFear to resemble those of cholesterol [13]
and mdfitin [42], to some extent.
In condufion it may be stated that the studies
presen~d in this paper reve~ that the complex
effects of lutdn on mitochondfi~ function [7]
reflect the membran~pe~urbing action of the
hpophfl~ Shuttling of protons across the
mitochondfi~ membrane as demanded by the
chemiosmot~ hypothesis [43] is a function which
lutein is unlikdy to perform because of its struc~
ural peculiaritie~
~ o ~ m ~
The authors thank Dr. G. Govil, Tata Instim~
of Fundamem~ R ~ e a ~
Bomba~ and Dr.
K.R.K. Easwaran and Dr. P. B ~ a m of the
M~d~
B~phyfi~ Unit of t~s Instim~ ~ r use
of ~ o r laboratory eq~pmems.
R~e~nc~
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