The effect of vitamin E on the structure of membrane lipid assemblies

The effects of vitamin E on the activity of membrane-dependent enzymes suggest that it acts indirectly by modifying some properties of the lipid host. The effects of α-tocopherol (α-T) and α-tocopherol hemisuccinate (α-THS) on phospholipid monolayer structure, curvature, and bending elasticity were examined using X-ray diffraction and the osmotic stress method. These ligands were mixed with the hexagonal phase-forming lipid, dioleoylphosphatidylethanolamine (DOPE). Increasing levels up to 50 mol% α-T in DOPE in excess water result in a systematic decrease in the lattice dimension. Analysis of the structural changes imposed by α-T shows that it contributes a spontaneous radius of curvature of −13.7 Å. This unusually negative value is comparable to diacylglycerols. α-T does not affect the bending elasticity of these monolayers. α-THS in its charged form decreases membrane curvature, but in its undissociated neutral form has a qualitatively similar but reduced effect on monolayer curvature, as does α-T.We discuss these results in terms of the local stresses such ligands would produce in the vicinity of a membrane protein, and how one might expect proteins to respond to such stress. The effects of vitamin E on the activity of membrane-dependent enzymes suggest that it acts indirectly by modifying some properties of the lipid host. The effects of α-tocopherol (α-T) and α-tocopherol hemisuccinate (α-THS) on phospholipid monolayer structure, curvature, and bending elasticity were examined using X-ray diffraction and the osmotic stress method. These ligands were mixed with the hexagonal phase-forming lipid, dioleoylphosphatidylethanolamine (DOPE). Increasing levels up to 50 mol% α-T in DOPE in excess water result in a systematic decrease in the lattice dimension. Analysis of the structural changes imposed by α-T shows that it contributes a spontaneous radius of curvature of −13.7 Å. This unusually negative value is comparable to diacylglycerols. α-T does not affect the bending elasticity of these monolayers. α-THS in its charged form decreases membrane curvature, but in its undissociated neutral form has a qualitatively similar but reduced effect on monolayer curvature, as does α-T. We discuss these results in terms of the local stresses such ligands would produce in the vicinity of a membrane protein, and how one might expect proteins to respond to such stress. α-Tocopherol (α-T) has been shown to have two major roles in membranes since it was first discovered 1) as a lipid-soluble antioxidant that acts to prevent free radical damage of polyunsaturated fatty acids (1Bisby R.H. Interactions of vitamin E with free radicals and membranes.Free Radic. Res. Commun. 1990; 8: 299-306Google Scholar, 2Burton G.W. Foster D.O. Perly B. Slater T.F. Smith I.C.P. Ingold K.U. Biological antioxidants.Philos. Trans. R. Soc. Lond. Biol. Sci. 1985; 311: 565-578Google Scholar, 3Srivastava S. Phadke R.S. Govil G. Rao C.N.R. Fluidity, permeability and antioxidant behaviour of model membranes incorporated with alpha-tocopherol and vitamin E acetate.Biochim. Biophys. Acta. 1983; 734: 353-362Google Scholar, 4Burton G.W. Ingold K.U. Vitamin E: applications of the principles of physical organic chemistry to the exploration of its structure and function.Acc. Chem. Res. 1986; 19: 194-201Google Scholar, 5Burton G.W. Ingold K.U. Vitamin E as an in vitro and in vivo antioxidant.Ann. N. Y. Acad. Sci. 1989; 570: 7-22Google Scholar), and 2) as a membrane-stabilizing agent through its van der Waals interaction with membrane phospholipids. This latter ability to stabilize membranes may help to prevent the damaging actions of phospholipases, although this is still under debate (6Kagan V. Tocopherol stabilizes membrane against phospholipase A, free fatty acids, and lysophospholipids.Ann. N. Y. Acad. Sci. 1989; 570: 121-135Google Scholar, 7Salgado J. Villalian J. Gomez-Fernandez J.C. Alpha-tocopherol interacts with natural micelle-forming the Biophys. Scholar, Vitamin E and its in Res. Scholar, of membranes by alpha-tocopherol against the damaging of of of vitamin Res. 1986; Scholar, V. J. structural of a of phospholipase by alpha-tocopherol and its in structure of the phospholipase and alpha-tocopherol Biol. α-T has been shown to Vitamin E: Res. Scholar, R. S. S. to Scholar, of with and is of its antioxidant Acad. Sci. Scholar), to the but by the of the to the membrane R. of activity by and Biophys. These and such as of the effect of α-T on of in by with Soc. 8: Scholar, Vitamin E in through an of Biophys. Acta. Scholar), Vitamin E the of in J. Scholar), and phospholipase of phospholipase activity by neutral in and by in Biophys. Acta. suggest that the of activity may have to with the effect has on membrane structure, as these enzymes on that in membranes to a membrane hemisuccinate (α-THS) activity and has been as a agent with Vitamin E in in Res. has been shown that this through a of such as and of and of its Vitamin E: of as and α-THS the by a to the and it is this that the antioxidant activity of α-T. is to with membrane and the of hemisuccinate on the properties of Biophys. Acta. α-T and α-THS may activity by the properties of the it is of to effect the of these has on the structure of lipid the effect of α-T and α-THS on such the of X-ray diffraction to the by lipid membranes The of and phospholipid membrane curvature and bending J. S. R. of activity by membrane curvature and J. and R. and physical of to an Biophys. Acta. Scholar, R. of activity by the physical properties of lipid an curvature Scholar, of by curvature, and have shown that curvature the activity of membrane enzymes in We have the of α-T and α-THS on the spontaneous curvature and bending to dioleoylphosphatidylethanolamine lipid monolayers. the of membrane such model as to the properties of membrane that was by of natural and was by α-THS was and was The of α-THS was by of a of a α-THS with in The was with and in DOPE was and DOPE and α-T were under α-THS was and water in was lipid were by the of DOPE with α-T α-THS in The was by under a of by The lipid were to by of water excess of of osmotic The were to The were two with an X-ray of and examined by X-ray the by the lipid an X-ray diffraction was a was using a The diffraction of the lipid were using X-ray The of the was by and that hexagonal by X-ray with the to the of the first lattice of of the hexagonal to on one hexagonal with the water on the and with lipid the of the lattice is with the an of its lattice as shown in the of lipid and This the by and V. X-ray diffraction of Biol. and on of the of the and of the and structural the lipid in this in and structural of in this of α-THS is an on the of α-T α-tocopherol of α-THS is an on the of α-T in a The water and lipid through the of an the in of the water is this and of the lipid is The radius of this water is to the of the water in the and as in 1) The lipid the is in 2) is the of the lipid is the of water using the in the of a lipid is it is on the of an one DOPE of is the of α-T and is the of α-T to phospholipids. The is in The and the radius the by in and is a of a in a form that and S. effects of on structural and properties of phospholipid J. a results the has a that has a and is as the The of the the of the to the of curvature of the monolayers. the spontaneous curvature of the lipid monolayers. has been the mixed the curvature of the using it is the α-T is by S. effects of on structural and properties of phospholipid J. the is the free of the by the of bending properties of lipid and Scholar, model of the to hexagonal of lipid Scholar), as shown in is the bending is the and and the and the spontaneous the free of the lipid under of osmotic with the osmotic by the osmotic stress a of the the monolayer of phospholipid hexagonal Chem. Soc. 1986; Scholar, curvature, lipid and structural under 1990; Scholar), as shown in mol% α-T α-THS in DOPE and the lattice of the is shown in α-T and the of the decreases with that α-T and α-THS the curvature of the mixed α-T of the lattice hexagonal lattice lipid of of α-tocopherol (α-T) α-tocopherol hemisuccinate (α-THS) and α-T in dioleoylphosphatidylethanolamine the of α-T with DOPE shown in The is shown as it with lipid in the with water a is on the α-T were and hexagonal The of lipid the was the of the excess with the in excess as a of water the by DOPE and the and a the in lattice with α-T and was by systematic of lipid and the of The of this that is a of these a in the monolayer that does not as the monolayer is The of this is by the of the in α-T in DOPE is the lipid and of a the of the its and its the and this spontaneous of the lipid is and using the in excess the lattice and the value of that α-T monolayer The the spontaneous curvature of the to α-T is −13.7 it a membrane with one of the negative in the of the and negative DOPE is is with The of and phospholipid membrane curvature and bending J. Scholar, V. X-ray diffraction of Biol. These curvature shown in of spontaneous monolayer curvature, as a of α-T of spontaneous of curvature and bending radius of in a the a of how it is to these as water is the of these to the of the The in that α-T does not the bending elasticity of these the osmotic to the of with the in monolayer curvature The by the of the bending and of α-T in DOPE have the modifying effects of α-T on phospholipid with the that such may to an of the by α-T the activity of membrane as of α-T has not been it is that the physical properties of the lipid curvature is one physical that is to produce local stress in membranes and affect and is that of S. R. of activity by membrane curvature and J. Scholar), to on the curvature of its lipid We have the of of This is by the stress spontaneous curvature of lipid The this curvature, the local stress a lipid produce to a and the the in We have this in changes that a and might to the of lipid with negative curvature in its enzymes by α-T Vitamin E: Res. Scholar, R. S. S. to Scholar, of with and is of its antioxidant Acad. Sci. Scholar), and that may a result of a effect has on membrane this have shown that α-T has one of the and contributes one of the negative in comparable to that of the The effects of and of and on membrane monolayer J. to on enzymes is through the local curvature it in the vicinity of these This curvature stress results the of to the of the membrane to the might expect that proteins in the of α-T would to this stress. would result a a of the to the of the This is the shown in the does not affect the of the membrane monolayers. is to local of the monolayer as might by the in to of the not but the effects that it has on local curvature α-T the hexagonal lattice of the of a spontaneous curvature that of a of the The form of the although effect on the DOPE lattice as α-T. it as it were and its negative curvature α-T α-Tocopherol (α-T) has been shown to have two major roles in membranes since it was first discovered 1) as a lipid-soluble antioxidant that acts to prevent free radical damage of polyunsaturated fatty acids (1Bisby R.H. Interactions of vitamin E with free radicals and membranes.Free Radic. Res. Commun. 1990; 8: 299-306Google Scholar, 2Burton G.W. Foster D.O. Perly B. Slater T.F. Smith I.C.P. Ingold K.U. Biological antioxidants.Philos. Trans. R. Soc. Lond. Biol. Sci. 1985; 311: 565-578Google Scholar, 3Srivastava S. Phadke R.S. Govil G. Rao C.N.R. Fluidity, permeability and antioxidant behaviour of model membranes incorporated with alpha-tocopherol and vitamin E acetate.Biochim. Biophys. Acta. 1983; 734: 353-362Google Scholar, 4Burton G.W. Ingold K.U. Vitamin E: applications of the principles of physical organic chemistry to the exploration of its structure and function.Acc. Chem. Res. 1986; 19: 194-201Google Scholar, 5Burton G.W. Ingold K.U. Vitamin E as an in vitro and in vivo antioxidant.Ann. N. Y. Acad. Sci. 1989; 570: 7-22Google Scholar), and 2) as a membrane-stabilizing agent through its van der Waals interaction with membrane phospholipids. This latter ability to stabilize membranes may help to prevent the damaging actions of phospholipases, although this is still under debate (6Kagan V. Tocopherol stabilizes membrane against phospholipase A, free fatty acids, and lysophospholipids.Ann. N. Y. Acad. Sci. 1989; 570: 121-135Google Scholar, 7Salgado J. Villalian J. Gomez-Fernandez J.C. Alpha-tocopherol interacts with natural micelle-forming the Biophys. Scholar, Vitamin E and its in Res. Scholar, of membranes by alpha-tocopherol against the damaging of of of vitamin Res. 1986; Scholar, V. J. structural of a of phospholipase by alpha-tocopherol and its in structure of the phospholipase and alpha-tocopherol Biol. α-T has been shown to Vitamin E: Res. Scholar, R. S. S. to Scholar, of with and is of its antioxidant Acad. Sci. Scholar), to the but by the of the to the membrane R. of activity by and Biophys. These and such as of the effect of α-T on of in by with Soc. 8: Scholar, Vitamin E in through an of Biophys. Acta. Scholar), Vitamin E the of in J. Scholar), and phospholipase of phospholipase activity by neutral in and by in Biophys. Acta. suggest that the of activity may have to with the effect has on membrane structure, as these enzymes on that in membranes to a membrane α-Tocopherol hemisuccinate (α-THS) activity and has been as a agent with Vitamin E in in Res. has been shown that this through a of such as and of and of its Vitamin E: of as and α-THS the by a to the and it is this that the antioxidant activity of α-T. is to with membrane and the of hemisuccinate on the properties of Biophys. Acta. α-T and α-THS may activity by the properties of the it is of to effect the of these has on the structure of lipid the effect of α-T and α-THS on such the of X-ray diffraction to the by lipid membranes The of and phospholipid membrane curvature and bending J. S. R. of activity by membrane curvature and J. and R. and physical of to an Biophys. Acta. Scholar, R. of activity by the physical properties of lipid an curvature Scholar, of by curvature, and have shown that curvature the activity of membrane enzymes in We have the of α-T and α-THS on the spontaneous curvature and bending to dioleoylphosphatidylethanolamine lipid monolayers. the of membrane such model as to the properties of membrane that α-T. was by of natural and was by α-THS was and was The of α-THS was by of a of a α-THS with in The was with and in DOPE was and DOPE and α-T were under α-THS was and water in was lipid were by the of DOPE with α-T α-THS in The was by under a of by The lipid were to by of water excess of of osmotic The were to The were two with an X-ray of and examined by X-ray the by the lipid an X-ray diffraction was a was using a The diffraction of the lipid were using X-ray The of the was by and that hexagonal by X-ray with the to the of the first lattice of of the hexagonal to on one hexagonal with the water on the and with lipid the of the lattice is with the an of its lattice as shown in the of lipid and This the by and V. X-ray diffraction of Biol. and on of the of the and of the and structural the lipid in this in and structural of in this of α-THS is an on the of α-T α-tocopherol of α-THS is an on the of α-T in a The water and lipid through the of an the in of the water is this and of the lipid is The radius of this water is to the of the water in the and as in 1) The lipid the is in 2) is the of the lipid is the of water using the in the of a lipid is it is on the of an one DOPE of is the of α-T and is the of α-T to phospholipids. The is in The and the radius the by in and is a of a in a form that and S. effects of on structural and properties of phospholipid J. a results the has a that has a and is as the The of the the of the to the of curvature of the monolayers. the spontaneous curvature of the lipid monolayers. has been the mixed the curvature of the using it is the α-T is by S. effects of on structural and properties of phospholipid J. the is the free of the by the of bending properties of lipid and Scholar, model of the to hexagonal of lipid Scholar), as shown in is the bending is the and and the and the spontaneous the free of the lipid under of osmotic with the osmotic by the osmotic stress a of the the monolayer of phospholipid hexagonal Chem. Soc. 1986; Scholar, curvature, lipid and structural under 1990; Scholar), as shown in was by of natural and was by α-THS was and was The of α-THS was by of a of a α-THS with in The was with and in DOPE was and DOPE and α-T were under α-THS was and water in was lipid were by the of DOPE with α-T α-THS in The was by under a of by The lipid were to by of water excess of of osmotic The were to The were two with an X-ray of and examined by X-ray α-T was by of natural and was by α-THS was and was The of α-THS was by of a of a α-THS with in The was with and in DOPE was and DOPE and α-T were under α-THS was and water in was The lipid were by the of DOPE with α-T α-THS in The was by under a of by The lipid were to by of water excess of of osmotic The were to The were two with an X-ray of and examined by X-ray X-ray the by the lipid an X-ray diffraction was a was using a The diffraction of the lipid were using X-ray The of the was by and that hexagonal by X-ray with the to the of the first lattice of of the hexagonal to on one the by the lipid an X-ray diffraction was a was using a The diffraction of the lipid were using X-ray The of the was by and that hexagonal by X-ray with the to the of the first lattice of of the hexagonal to on one hexagonal with the water on the and with lipid the of the lattice is with the an of its lattice as shown in the of lipid and This the by and V. X-ray diffraction of Biol. and on of the of the and of the and structural the lipid in this in and structural of in this of α-THS is an on the of α-T α-tocopherol of α-THS is an on the of α-T in a The water and lipid through the of an the in of the water is this and of the lipid is The radius of this water is to the of the water in the and as in 1) The lipid the is in 2) is the of the lipid is the of water using the in the of a lipid is it is on the of an one DOPE of is the of α-T and is the of α-T to phospholipids. The is in The and the radius the by in and is a of a in a form that and S. effects of on structural and properties of phospholipid J. a results the has a that has a and is as the The of the the of the to the of curvature of the monolayers. the spontaneous curvature of the lipid monolayers. has been the mixed the curvature of the using it is the α-T is by S. effects of on structural and properties of phospholipid J. the is the free of the by the of bending properties of lipid and Scholar, model of the to hexagonal of lipid Scholar), as shown in is the bending is the and and the and the spontaneous the free of the lipid under of osmotic with the osmotic by the osmotic stress a of the the monolayer of phospholipid hexagonal Chem. Soc. 1986; Scholar, curvature, lipid and structural under 1990; Scholar), as shown in hexagonal with the water on the and with lipid the of the lattice is with the an of its lattice as shown in the of lipid and This the by and V. X-ray diffraction of Biol. and on of the of the and of the and structural the lipid in this in α-tocopherol The water and lipid through the of an the in of the water is this and of the lipid is The radius of this water is to the of the water in the and as in 1) The lipid the is in 2) is the of the lipid is the of water using the in the of a lipid is it is on the of an one DOPE of is the of α-T and is the of α-T to phospholipids. The is in The and the radius the by in and is a of a in a form that and S. effects of on structural and properties of phospholipid J. a results the has a that has a and is as the The of the the of the to the of curvature of the monolayers. the spontaneous curvature of the lipid monolayers. has been the mixed the curvature of the using it is the α-T is by S. effects of on structural and properties of phospholipid J. the is the free of the by the of bending properties of lipid and Scholar, model of the to hexagonal of lipid Scholar), as shown in is the bending is the and and the and the spontaneous the free of the lipid under of osmotic with the osmotic by the osmotic stress a of the the monolayer of phospholipid hexagonal Chem. Soc. 1986; Scholar, curvature, lipid and structural under 1990; Scholar), as shown in mol% α-T α-THS in DOPE and the lattice of the is shown in α-T and the of the decreases with that α-T and α-THS the curvature of the mixed α-T the of α-T with DOPE shown in The is shown as it with lipid in the with water a is on the α-T were and hexagonal The of lipid the was the of the excess with the in excess as a of water the by DOPE and the and a the in lattice with α-T and was by systematic of lipid and the of The of this that is a of these a in the monolayer that does not as the monolayer is The of this is by the of the in α-T in DOPE is the lipid and of a the of the its and its the and this spontaneous of the lipid is and using the in excess the lattice and the value of that α-T monolayer The the spontaneous curvature of the to α-T is −13.7 it a membrane with one of the negative in the of the and negative DOPE is is with The of and phospholipid membrane curvature and bending J. Scholar, V. X-ray diffraction of Biol. These curvature shown in of spontaneous monolayer curvature, as a of α-T of spontaneous of curvature and bending radius of in a the a of how it is to these as water is the of these to the of the The in that α-T does not the bending elasticity of these the osmotic to the of with the in monolayer curvature The by the of the bending and of α-T in DOPE The mol% α-T α-THS in DOPE and the lattice of the is shown in α-T and the of the decreases with that α-T and α-THS the curvature of the mixed α-T the of α-T with DOPE shown in The is shown as it with lipid in the with water a is on the α-T were and hexagonal The of lipid the was the of the excess with the in excess the of The of this that is a of these a in the monolayer that does not as the monolayer is The of this is by the of the in α-T in DOPE is The spontaneous of the lipid is and using the in excess the lattice and the value of that α-T monolayer The the spontaneous curvature of the to α-T is −13.7 it a membrane with one of the negative in the of the and negative DOPE is is with The of and phospholipid membrane curvature and bending J. Scholar, V. X-ray diffraction of Biol. These curvature shown in radius of the a of how it is to these as water is the of these to the of the The in that α-T does not the bending elasticity of these monolayers. have the modifying effects of α-T on phospholipid with the that such may to an of the by α-T the activity of membrane as of α-T has not been it is that the physical properties of the lipid curvature is one physical that is to produce local stress in membranes and affect and is that of S. R. of activity by membrane curvature and J. Scholar), to on the curvature of its lipid We have the of of This is by the stress spontaneous curvature of lipid The this curvature, the local stress a lipid produce to a and the the in We have this in enzymes by α-T Vitamin E: Res. Scholar, R. S. S. to Scholar, of with and is of its antioxidant Acad. Sci. Scholar), and that may a result of a effect has on membrane this have shown that α-T has one of the and contributes one of the negative in comparable to that of the The effects of and of and on membrane monolayer J. to on enzymes is through the local curvature it in the vicinity of these This curvature stress results the of to the of the membrane to the might expect that proteins in the of α-T would to this stress. would result a a of the to the of the This is the shown in the does not affect the of the membrane monolayers. is to local of the monolayer as might by the in to of the not but the effects that it has on local curvature α-T the hexagonal lattice of the of a spontaneous curvature that of a of the The form of the although effect on the DOPE lattice as α-T. it as it were and its negative curvature α-T We have the modifying effects of α-T on phospholipid with the that such may to an of the by α-T the activity of membrane as of α-T has not been it is that the physical properties of the lipid curvature is one physical that is to produce local stress in membranes and affect and is that of S. R. of activity by membrane curvature and J. Scholar), to on the curvature of its lipid We have the of of This is by the stress spontaneous curvature of lipid The this curvature, the local stress a lipid produce to a and the the in We have this in enzymes by α-T Vitamin E: Res. Scholar, R. S. S. to Scholar, of with and is of its antioxidant Acad. Sci. Scholar), and that may a result of a effect has on membrane this have shown that α-T has one of the and contributes one of the negative in comparable to that of the The effects of and of and on membrane monolayer J. to on enzymes is through the local curvature it in the vicinity of these This curvature stress results the of to the of the membrane to the might expect that proteins in the of α-T would to this stress. would result a a of the to the of the This is the shown in the α-T does not affect the of the membrane monolayers. is to local of the monolayer as might by the in to of the We not but the effects that it has on local curvature α-T the hexagonal lattice of the of a spontaneous curvature that of a of the The form of the although effect on the DOPE lattice as α-T. it as it were and its negative curvature α-T and the of the and of α-tocopherol α-tocopherol hemisuccinate dioleoylphosphatidylethanolamine hexagonal bending

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