Ligustilide, a major bioactive component of Angelica sinensis, promotes bone formation via the GPR30/EGFR pathway

Angelica sinensis (Oliv.) Diels is a widely-used traditional Chinese herbal medicine in treating osteoporosis. Ligustilide (LIG) is the main component of A. sinensis and is considered to be the most effective biologically active ingredient in this plant. LIG has been found to have multiple pharmacological activities, such as anti-atherosclerosis, neuroprotection, anticancer, anti-inflammatory and analgesic. However, little is known regarding its anti-osteoporotic effects. The aims of this study were to investigate any protective effect of LIG on bone formation. The results showed that LIG significantly ameliorated inhibition of bone formation in zebrafish caused by prednisolone. LIG promoted osteoblast differentiation, including that of the pre-osteoblastic cell line MC3T3-E1 and bone marrow mesenchymal stem cells. LIG greatly improved the viability of MC3T3-E1 cells exposed to H₂O₂, attenuated H₂O₂-induced apoptosis and increased the expression of Bcl-2. Furthermore, LIG treatment lead to marked activation of phosphorylated EGFR and ERK1/2. These effects could be obviously inhibited by blocking GPR30 signaling with the specific inhibitor G15. Collectively, the results reveal that GPR30 is a positive switch for LIG to increase bone formation via regulation of EGFR, and these results provide evidence for the potential of LIG to treat osteoporosis.

Cancer risk from low dose radiation depends directly on the organ mass in a general model of radiation-induced cancer risk

Current methods of evaluating radiation-induced cancer risk depend on the organ dose but not explicitly on extensive quantities such as the organ mass. However, at the same organ dose, one may expect the larger number of cells in a larger organ to lead to a higher cancer risk. Here the author introduces organ- and radiation type-specific cell cancer risk coefficients and obtains analytical relations between cancer risk and the radiation environment, which contains the dependence of cancer risk on organ masses. The excess cancer risk induced by low dose radiation for an organ is shown to be directly proportional to the organ mass. Therefore the total excess risk for all solid cancers depends directly on organ masses and consequently on body weight or size. This method is also being compared with three existing methods of evaluating the radiation-induced cancer risk, and special cases where this formulation matches each method are demonstrated. The results suggest that the direct dependence of cancer risk on organ masses needs to be checked against existing epidemiological data and, if verified, should be included in the methodology for the evaluation of radiation-induced cancer risk, in particular the individual risk. This dependence is also expected to affect the cancer risk transport from one population group to another that is different in organ mass, body weight or height.

Incoherent c-axis interplane response of the iron chalcogenide FeTe(0.55)Se(0.45) superconductor from infrared spectroscopy

We report on the interplane c-axis electronic response of FeTe(0.55)Se(0.45) investigated by infrared spectroscopy. We find that the normal-state c-axis electronic response of FeTe(0.55)Se(0.45) is incoherent and bears significant similarities to those of mildly underdoped cuprates. The c-axis optical conductivity σ(c)(ω) of FeTe(0.55)Se(0.45) does not display well-defined Drude response at all temperatures. As temperature decreases, σ(c)(ω) is continuously suppressed. The incoherent c-axis response is found to be related to the strong dissipation in the ab-plane transport: a pattern that holds true for various correlated materials as well as FeTe(0.55)Se(0.45).

The radiation environment on the Moon from galactic cosmic rays in a lunar habitat

We calculated how the radiation environment in a habitat on the surface of the Moon would have depended on the thickness of the habitat in the 1977 galactic cosmic-ray environment. The Geant4 Monte Carlo transport code was used, and a hemispherical dome made of lunar regolith was used to simulate the lunar habitat. We investigated the effective dose from primary and secondary particles including nuclei from protons up to nickel, neutrons, charged pions, photons, electrons and positrons. The total effective dose showed a strong decrease with the thickness of the habitat dome. However, the effective dose values from secondary neutrons, charged pions, photons, electrons and positrons all showed a strong increase followed by a gradual decrease with the habitat thickness. The fraction of the summed effective dose from these secondary particles in the total effective dose increased with the habitat thickness, from approximately 5% for the no-habitat case to about 47% for the habitat with an areal thickness of 100 g/cm(2).

Effects of Nuclear Cross Sections at Different Energies on the Radiation Hazard from Galactic Cosmic Rays

The radiation hazard for astronauts from galactic cosmic rays (GCR) is a major obstacle to long-duration human space exploration. Space radiation transport codes have been developed to calculate the radiation environment on missions to the Moon, Mars, and beyond. We have studied how uncertainties in fragmentation cross sections at different energies affect the accuracy of predictions from such radiation transport calculations. We find that, in deep space, cross sections at energies between 0.3 and 0.85 GeV/nucleon have the largest effect in solar maximum GCR environments. At the International Space Station, cross sections at higher energies have the largest effect due to the geomagnetic cutoff.

High LET-induced H2AX phosphorylation around the Bragg curve

We investigated the spatial distribution of the induction of the phosphorylated form of the histone protein H2AX (gamma-H2AX), known to be activated by DSBs. Following irradiation of human fibroblast cells with 600 MeV/nucleon silicon and 600 MeV/nucleon iron ions we observed the formation of gamma-H2AX aggregates in the shape of streaks stretching over several micrometers in an x/y plane. Polyethylene shielding was used to achieve a Bragg curve distribution with beam geometry parallel to the monolayer of cells. We present data that highlights the formation of immunofluorescent gamma-H2AX tracks showing the ion trajectories across the Bragg peak of irradiated human fibroblast cells. Qualitative analyses of these distributions indicated potentially increased clustering of DNA damage before the Bragg peak, enhanced gamma-H2AX distribution at the peak, and provided visual evidence of high-linear energy transfer particle traversal of cells beyond the Bragg peak in agreement with one-dimensional transport approximations. Spatial assessment of gamma-H2AX fluorescence may provide direct insights into DNA damage across the Bragg curve for high charge and energy ions including the biological consequences of shielding and possible contributors to bystander effects.

Constituents from Lethariella cladonioides

The isolation from the acetone extract of Lethariella cladonioides of the new compound cladonioidesin (1) and 10 other constituents is reported.

Cytotoxic 7,20-epoxy ent-kauranoids from Isodon xerophilus

Four 7,20-epoxy ent-kaurane diterpenoids, xerophilusins G (1) and I-K (2-4), were isolated from the leaves of Isodon xerophilus, along with four known ones, enanderianin C (5), rosthorin A (6), longikaurin B (7), and rabdoternin D (8). Their structures were determined primarily using NMR spectroscopic techniques. The structure and stereochemistry of 3 were confirmed by X-ray crystallography. Compounds 4 and 7 exhibited broad cytotoxicity against four kinds of human tumor cells (K562, HL-60, HCT, and MKN-28 cells) in the range of 2.23-15.35 and 0.30-8.61 microg/ml, respectively.

Kinetic equation with exact charge conservation

A kinetic master equation for multiplicity distributions is formulated for charged particles which are created or destroyed only in pairs due to the conservation of their Abelian charge. It allows one to study time evolution of the multiplicity distributions in a relativistic many-body system with arbitrary average particle multiplicities. It is shown to reproduce the equilibrium results for both canonical (rare particles) and grand canonical (abundant particles) systems. For canonical systems, the equilibrium multiplicity is much lower and the relaxation time is much shorter than the naive extrapolation from grand canonical results. Implications for chemical equilibration in heavy-ion collisions are also discussed.

Sterols from the fungus Lactarium volemus

Seven ergostane-type sterols and two mono-glucosides were isolated from the ethyl acetate soluble fraction of Lactarium rolemus. Three are previously unknown, i.e. 3-O-beta-D-glucopyranosyl-22E,24R-5alpha,8alpha-epidioxyergosta-6,22-diene, 3-O-beta-D-glucopyranosyl-22E,24R-5beta,8beta-epidioxyergosta-6,22-diene and 22E,24R-ergosta-7,22-diene-3beta,5alpha,6beta,9alpha-tetraol. The structural elucidation of these compounds was mainly achieved by spectroscopic methods.

Constituents from Limonia crenulata

A new indole alkaloid, crenulatine (1), along with twenty known compounds, was isolated from the stems of Limonia Crenulata. Their structures were identified by spectral means. Those compounds include four alkaloids, four coumarins, two flavanones, three tetranortriterpenoids, one triterpenoid, three steroids, two lignans and two aromatic compounds.

Constituents of Craspedolobium schochii

Nine phenolic compounds, including a new one, were isolated from 70% acetone extract of Craspedolobium schochii. The new compound was identified as 3-(3,4-dimethoxy-2-hydroxyphenyl)-7-hydroxy-coumarin (1) on the basis of spectroscopic evidence.

New steroids from Clerodendrum colebrookianum

Five new steroids, colebrin A-E (1-5) were isolated from the aerial parts of Clerodendrum colebrookianum. The structures of the new compounds were elucidated on the basis of spectral evidence.

Gallotannins and related polyphenols from Pistacia weinmannifolia

Two new gallotannins, pistafolins A (1) and B (2), were isolated from the leaf extract of Pistacia weinmannifolia. Their structures were determined by spectral methods. Four known gallotannins (3-6), seven known flavonoid glycosides (7-13), along with 1-O-beta-D-(6'-O-galloyl)-glucopyranosyl-3-methoxy-5-hydroxybenzen e (14), gallic acid (15), methyl gallate (16), (+)-catechin (17), and (+)-gallocatechin (18), were also isolated. Some of these compounds were tested for their cytotoxicity toward K562 cells, and two small molecular phenolic compounds, 15 and 18, showed significant inhibitory effects with IC50 values less than 5 micrograms/ml.

A new ent-kaurane diterpenoid from Isodon phyllostachys

A new ent-kaurane diterpenoid, phyllostachysin C (1), together with five known compounds, sculponeatins B and C, nodosin, ursolic acid and 2 alpha-hydroxyursolic acid, were isolated from the leaves of Isodon phyllostachys. The structure of 1 was elucidated on the basis of its spectral properties.

New 7,20:14,20-diepoxy ent-kauranoids from Isodon xerophilus

Three new 7,20:14,20-diepoxy-ent-kaurane diterpenoids, xerophilusins A-C (1-3), together with a known one, macrocalin B (4), were isolated from the leaves of Isodon xerophilus. Their structures were elucidated on the basis of their spectral properties and X-ray crystallographic analysis. Compounds 1, 2, and 4 showed significant cytotoxic activity against K562, HL-60, and MKN-28 cells.

Hydrolyzable tannins and related polyphenols from Eucalyptus globulus

Eucaglobulin (1), a new complex of gallotannin and monoterpene, was isolated from the leaves of Eucaloptus globulus. Its structure was elucidated on the basis of spectral data. Four known hydrolyzable tannins [tellimagrandin I (2), eucalbanin C (3), 2-O-digalloyl-1,3,4-tri-O-galloyl-beta-D-glucose (4), 6-O-digalloyl-1,2,3-tri-O-galloyl-beta-D-glucose (5)], as well as gallic acid (6) and (+)-catechin (7), were also isolated. The antibacterial effects of some of these compounds were examined.

Colebroside A, a new diglucoside of fatty acid ester of glycerin from Clerodendrum colebrookianum

Colebroside A (1), a new diglucoside of fatty acid ester of glycerin, was isolated from the aerial parts of Clerodendrum colebrookianum Walp., along with nine known compounds (2-10). Their structures were elucidated by spectroscopic and chemical methods. Compounds 2, 3, 4, 5, 7, 8, 9 and 10 have been obtained from this plant for the first time.

Diterpenoids from Isodon leucophyllus

The structures of two new ENT-kaurane diterpenoids and two derivatives of shikokianin isolated from leaves of Isodon leucophyllus were elucidated by 1D and 2D NMR techniques as 11alpha-acetoxyeffusanin D, 6-acetylepinodosinol, 16beta-ethoxymethyleneshikokianin, and 16alpha-ethoxymethyleneshi-kokianin.

Diterpenoids from isodon eriocalyx

Three new diterpenoids, eriocalyxins C-E (1-3), were isolated from Isodon eriocalyx. Their structures were elucidated as 6beta-hydroxy-15beta-acetoxy-3alpha,20-epoxy-16beta, 17-epoxy-ent-kaur-1,7-dione (1), 1alpha,7beta-dihydroxy-6beta, 15beta-diacetoxy-7,20-epoxy-ent-kaur-16-ene (2), and 15beta-acetoxy-1,6-dioxo-6,7-seco-ent-kaur-2,16-dien-7,20-olide (3), respectively, by means of spectroscopic methods, including one- and two-dimensional NMR techniques.

Chemical constituents of Isodon melissoides

Four new diterpenoids, melissoidesin E (1), F (2), G (4) and H (5), together with one known diterpenoid and two lignan glycosides, were isolated from aerial parts of Isodon melissoides. Their structures were established by spectral analysis and comparison with related compounds. The lignan glycosides (compounds 7 and 8) were the first examples to be isolated from the genus Isodon plants.

Lignans from Kadsura angustifolia

A new dibenzocyclooctadiene lignan named angustifolin D (1) together with four known lignans: kadsulignan L (2), kadsulignan N (3), schisantherin P (4) and meso-dihydroguaiaretic acid (5) were isolated from the stems of Kadsura angustifolia. Their structures and stereochemistries were elucidated by spectral studies. Compounds 2 and 5 showed moderate platelet-activating factor (PAF) antagonistic activities with IC50 values of 2.6 x 10(-5) and 4.1 x 10(-5) M, respectively.

Glabcensin Q-U, five new ent-kaurane diterpenoids from Isodon angustifolius var. glabrescens

Examination of the diterpenoid constituents of the dried leaves of Isodon angustifolius var. glabrescens led to the isolation of five new ent-kaurane diterpenoids, named as glabcensin Q-U (2-6). The structures were elucidated on the basis of spectroscopic evidences.

Nigranoic acid, a triterpenoid from Schisandra sphaerandra that inhibits HIV-1 reverse transcriptase

An A ring-secocycloartene triterpenoid, nigranoic acid (3,4-secocycloarta-4(28),24-(Z)-diene-3,-26-dioic acid, (1) was isolated from the stems of Schisandra sphaerandra, a Chinese traditional medicinal plant. Its structure elucidation and unambiguous NMR spectral assignment were achieved by the combination of 1D- and 2D-NMR techniques with the aid of computer modeling. Nigranoic acid showed activity in several anti-HIV reverse transcriptase and polymerase assays.

Cytotoxic ent-kaurene diterpenoids from Isodon gesneroides

From Isodon gesneroides, three new cytotoxic diterpenoids, gesneroidins A, B and C, together with one known diterpenoid, dawoensin A, were isolated, and the structure determination and unambiguous assignment of their stereochemistry and NMR spectral data were made by a combination of one-and two-dimensional NMR techniques, computer modelling calculations and X-ray analysis.

Diterpenoids from Isodon eriocalyx var. laxiflora

Three new, seco-ent-kaurane diterpenoids, laxiflorins A, B and C, together with four known diterpenoids eriocalyxin B, oriodonin, and maeocrystals A and B, were isolated from the leaves of Isodon eriocalyx var. laxiflora. Their structures were assigned by a combination of one- and two-dimensional NMR techniques and computer modeling calculations. Laxiflorin C displayed weak cytotoxic activity.

Cytotoxic ent-kaurene diterpenoids from three Isodon species

From Isodon loxothyrsa, one new diterpenoid, loxothyrin A, together with one known diterpenoid, adenolin B, from I.pleiophyllus, three known diterpenoids, coetsoidins A, B and G, and from I. adenoloma, one known diterpenoid, longikaurin F, were isolated. The structure determination of loxothyrin A, and the unambiguous NMR spectral assignments of the known compounds were made by a combination of 1D and 2D NMR techniques and computer modelling calculations. The isolates showed potent cytotoxic activities.

Cytotoxic diterpenoids from Isodon megathyrsus

A new diterpenoid, megathyrin A, together with three known compounds, rabdocoetsins B, C, and D, were isolated from the leaves of Isodon megathyrsus, and their structures and nmr spectral data were assigned by a combination of one- and two-dimensional nmr techniques. These compounds displayed significant cytotoxic activity.

The RR1 gene of herpes simplex virus type 1 is uniquely trans activated by ICP0 during infection

As has been demonstrated for herpes simplex virus type 2, we show in this report that the herpes simplex virus type 1 ribonucleotide reductase large subunit (RR1) gene is trans activated in transient transfection assays by VP16 and ICP0 but not by ICP4. Deletion analysis demonstrated that responsiveness to induction to VP16 resides in an octamer/TAATGARAT sequence of the RR1 promoter and that the TATA box alone is sufficient to provide induction by ICP0. The induction of the RR1 gene by ICP0 but not by ICP4 suggested that it might be possible to identify the cis-acting element(s) responsive to ICP4 in an ICP4-inducible promoter. To this end, a series of chimeric promoters containing various portions of the regulatory sequences of the RR1 promoter and thymidine kinase (TK) promoter were constructed. The TK promoter is trans activated by both ICP0 and ICP4 in transient transfection assays and by ICP4 in infection. The data show that replacing the RR1 TATA region with the TK TATA region permits ICP4 inducibility even if the rest of the RR1 promoter elements remain intact. To test whether the RR1 gene is induced by ICP0 during infection, four mutant viruses were constructed. (i) TAATGARAT+ has the wild-type RR1 promoter driving chloramphenicol acetyltransferase (CAT) and the RR2 promoter driving the lacZ gene. The RR2 gene codes for the small subunit of the ribonucleotide reductase and is expressed as a beta gene. (ii) TAATGARAT- has a triple-base change in the octamer/TAATGARAT element which renders it unresponsive to VP16 trans activation, eliminating that portion of the activation of the RR1 gene. (iii) TAATGARAT- delta alpha 0 has a deletion of the alpha 0 gene. (iv) TAATGARAT- delta alpha 4 has a deletion of the alpha 4 gene. Infections were carried out in Vero cells at a multiplicity of infection of 10 per cell; cells were assayed for CAT and beta-galactosidase (beta-Gal) activities and for virus yields. The first two infections gave strong CAT and beta-Gal activities and high yields of progeny virus. Infection with the third virus showed no CAT activity but did produce high levels of beta-Gal activity and virus progeny. The fourth infection resulted in strong CAT activity but no beta-Gal activity or progeny virus. The data demonstrated that the RR1 promoter was activated in the absence of ICP4 but not in the absence of ICP0 in these infections.(ABSTRACT TRUNCATED AT 400 WORDS)

[Responses mediated by GABAA and GABAB receptors on the somatic membrane of toad dorsal root ganglion neurones]

Intracellular recordings were made from neurons in toad dorsal root ganglion in vitro. Bath application of GABA (10(-4)-10(-3) mol/L) elicited either depolarization or depolarization followed by hyperpolarization respectively in 79% and 10% of the neurons. The remaining 11% did not show any response. The GABA-induced depolarization, which was accompanied by an increase of membrane conductance and usually a shortening of action potential duration (ApD), could be blocked by bicuculline. The GABA-depolarization was enhanced by low Cl- Ringer or reduced by high Cl- Ringer The membrane potential was not affected by 10(-4) mol/L baclofen. On the other hand, shortening of ApD could be produced by baclofen, but not blocked by bicuculline. Our results suggested that GABAA and GABAB receptors coexist on the somatic membrane of toad dorsal root ganglion neurons and mediate the changes respectively in membrane potential and shortening of ApD. The mechanism underlying presynaptic inhibition in the terminals of the primary afferents was discussed.

Transbilayer distribution and mobility of phosphatidylinositol in human red blood cells

The present studies describe the distribution of phosphatidylinositol (PI) within the membrane bilayer of the human red blood cell (RBC) as well as its transbilayer mobility. The membrane bilayer distribution was determined by measuring the hydrolysis of PI in the exterior leaflet of the RBC membrane using a PI-specific phospholipase C and by extraction of PI from the exterior leaflet using bovine serum albumin. The transbilayer mobility of PI was measured by following the fate of radiolabeled PI which was first incorporated into the outer leaflet of the RBC membrane. Our results indicate that PI is asymmetrically distributed in the membrane, with approximately 80% located in the inner and 20% in the outer leaflet of the bilayer. The rate of transbilayer mobility of PI is similar to that for certain molecular species of phosphatidylcholine and much slower than that reported for the aminophospholipids in the RBC membrane.

Mapping of epitopes on Poa p I and Lol p I allergens with monoclonal antibodies

Allergen Poa p I isolated from the dialysed aqueous extract of Kentucky blue grass pollen by affinity chromatography with an anti-Lol p I murine monoclonal antibody (MAb) 290A-167 was previously shown to consist of a 35.8-kilodalton (kD) component with a pI of 6.4, designated as Poa p Ia, and a 33-kD component with a pI of 9.1, designated as Poa p Ib. The present study reports on the comparative antigenic analyses of these two components, using MAbs produced separately against Poa p I and Lol p I. Thus, anti-Poa p I MAbs 60 and 61 and anti-Lol p I MAb 290A-167 recognized Poa p Ia and Poa p Ib whereas anti-Poa p I MAbs 62, 63 and 64 and anti-Lol p I MAb 348A-6 recognized only Poa p Ia. The specificities of the MAbs were further resolved by comparing their respective abilities to inhibit the binding of 125I-Poa p I or 125I-Lol p I to the different MAbs prepared in the form of solid phase. These studies revealed that at least 4 distinct epitopes (designated as E1, E2, E3 and E4) were shared by both Poa p I and Lol p I. All 4 epitopes were present on Poa p Ia whereas only E1 and E3 were detected on Poa p Ib. E1 was recognized by MAbs 60 and 61, E2 by MAbs 62, 63 and 64, E3 by MAb 290A-167 and E4 by MAb 348A-6.(ABSTRACT TRUNCATED AT 250 WORDS)

Chlorpromazine inhibits vesiculation, alters phosphoinositide turnover and changes deformability of ATP-depleted RBCs

To delineate further the underlying mechanism by which amphiphilic drugs can modulate vesicle release from human RBCs, we studied the effect of chlorpromazine on erythrocyte vesiculation induced by ATP depletion. This was correlated with turnover of the phosphoinositides as well as RBC deformability during the process since phosphoinositide metabolism may be involved in shape regulation of RBCs. Echinocytic shape transformation and subsequent vesiculation of RBCs, which commonly occur during ATP depletion, were inhibited by chlorpromazine. Furthermore, with a newly developed two-dimensional thin-layer chromatography separation of RBC membrane phospholipids, we showed that chlorpromazine significantly decreased the dephosphorylation of phosphatidylinositol-4,5-bisphosphate (PIP2) in both ATP-depleted RBCs as well as in cells with partly maintained ATP levels. Concomitantly, there was a smaller increase in the relative amount of phosphatidylinositol. In addition, chlorpromazine also inhibited the decreased in RBC deformability as well as the shift of osmotic fragility that occurs during ATP depletion of erythrocytes.

Isolation and characterization of Poa p I allergens of Kentucky bluegrass pollen with a murine monoclonal anti-Lol p I antibody

The Poa p I allergens were isolated from the retentate fraction of a dialyzed preparation of an aqueous extract of Kentucky bluegrass pollen by means of a reverse immunosorbent prepared with a murine anti-Lol p I monoclonal antibody, Mab 290-A-167. By sodium dodecyl sulphate-polyacrylamide gel electrophoresis and preparative isoelectrofocusing, Poa p I was found to consist of a 35.8-kD component with an isoelectric point of 6.4 and a 33-kD component with one of 9.1 and designated as Poa p Ia (acidic) and Poa p Ib (basic), respectively. The relative protein content of these components was estimated from the intensity of the stained bands following sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Thus, Poa p Ia appeared to be the major protein constituent, and on Western immunoblot it also bound the monoclonal antibody to a greater extent than Poa p Ib. On the other hand, Poa p Ib was shown by Western immunoblot and autoradiographic analysis, to bind to a greater extent the IgE antibodies present in a pool of sera from grass-allergic individuals. Therefore, Poa p Ib was considered as the major allergenic component of Poa p I. By competitive inhibition of the radioallergosorbent test, it was demonstrated that the Mab inhibited the binding of Poa p I allergens to human IgE antibodies to the extent of 70%. Hence, it is suggested that Mab and human IgE antibodies recognize identical or closely related determinants of Poa p I allergens.

Relationship of membrane systems in muscle to isomyosin content

The structures and functions of the various subdivisions of the membrane systems of muscle are reviewed. Morphometric data have been recalculated using functional definitions of the membranes as identified by their proteins. Thus, the junctional coupling between the sarcoplasmic reticulum and T system is separated from the remaining longitudinal sarcoplasmic reticulum that bears the calcium ATPase protein. In addition, the morphometry of the membrane systems is related to the various muscle fiber types as defined histochemically and by protein isoforms. The relation of isomyosin type and membrane quantities are compared for guinea pig, chicken, frog, and lobster skeletal muscles and rat and rabbit cardiac muscles. Fiber plasticity is considered in terms of the mixing and matching of amounts and kinds of membranes and proteins.