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B J Litman

Publications and source records attributed to B J Litman.

At least 19 recordsLinked to original sources
PubMed2001

Optimization of receptor-G protein coupling by bilayer lipid composition I: kinetics of rhodopsin-transducin binding.

The role of membrane composition in modulating the rate of G protein-receptor complex formation was examined using rhodopsin and transducin (G(t)) as a model system. Metarhodopsin II (MII) and MII-G(t) complex formation rates were measured, in the absence of GTP, via flash photolysis for rhodopsin reconstituted in 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (18:0,18:1PC) and 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (18:0,22:6PC) bilayers, with and without 30 mol% cholesterol. Variation in bilayer lipid composition altered the lifetime of MII-G(t) formation to a greater extent than the lifetime of MII. MII-G(t) formation was fastest in 18:0,22:6PC and slowest in 18:0,18:1PC/30 mol% cholesterol. At 37 degrees C and a G(t) to photolyzed rhodopsin ratio of 1:1 in 18:0,22:6PC bilayers, MII-G(t) formed with a lifetime of 0.6 +/- 0.06 ms, which was not significantly different from the lifetime for MII formation. Incorporation of 30 mol% cholesterol slowed the rate of MII-G(t) complex formation by about 400% in 18:0,18:1PC, but by less than 25% in 18:0,22:6PC bilayers. In 18:0,22:6PC, with or without cholesterol, MII-G(t) formed rapidly after MII formed. In contrast, cholesterol in 18:0,18:1PC induced a considerable lag time in MII-G(t) formation after MII formed. These results demonstrate that membrane composition is a critical factor in determining the temporal response of a G protein-coupled signaling system.

Cholesterol↗
PubMed2001

Optimization of receptor-G protein coupling by bilayer lipid composition II: formation of metarhodopsin II-transducin complex.

The visual transduction system was used as a model to investigate the effects of membrane lipid composition on receptor-G protein coupling. Rhodopsin was reconstituted into large, unilamellar phospholipid vesicles with varying acyl chain unsaturation, with and without cholesterol. The association constant (K(a)) for metarhodopsin II (MII) and transducin (G(t)) binding was determined by monitoring MII-G(t) complex formation spectrophotometrically. At 20 degrees C, in pH 7.5 isotonic buffer, the strongest MII-G(t) binding was observed in 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (18:0,22:6PC), whereas the weakest binding was in 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (18:0,18:1PC) with 30 mol% cholesterol. Increasing acyl chain unsaturation from 18:0,18:1PC to 18:0,22:6PC resulted in a 3-fold increase in K(a). The inclusion of 30 mol% cholesterol in the membrane reduced K(a) in both 18:0,22:6PC and 18:0,18:1PC. These findings demonstrate that membrane compositions can alter the signaling cascade by changing protein-protein interactions occurring predominantly in the hydrophilic region of the proteins, external to the lipid bilayer. These findings, if extended to other members of the superfamily of G protein-coupled receptors, suggest that a loss in efficiency of receptor-G protein binding is a contributing factor to the loss of cognitive skills, odor and spatial discrimination, and visual function associated with n-3 fatty acid deficiency.

Cholesterol↗
PubMed2000

Effect of ethanol and osmotic stress on receptor conformation. Reduced water activity amplifies the effect of ethanol on metarhodopsin II formation.

The combined effects of ethanol and osmolytes on both the extent of formation of metarhodopsin II (MII), which binds and activates transducin, and on acyl chain packing were examined in rod outer segment disc membranes. The ethanol-induced increase in MII formation was amplified by the addition of neutral osmolytes. This enhancement was linear with osmolality. At 360 milliosmolal, the osmolality of human plasma, 50 mM ethanol was 2.7 times more potent than at 0 osmolality, demonstrating the importance of water activity in in vitro experiments dealing with ethanol potency. Ethanol disordered acyl chain packing, and increasing osmolality enhanced this acyl chain disordering. Prior osmotic stress data showed a release of 35 +/- 2 water molecules upon MII formation. Ethanol increases this number to 49 water molecules, suggesting that ethanol replaces 15 additional water molecules upon MII formation. Amplification of ethanol effects on MII formation and acyl chain packing by osmolytes suggests that ethanol increases the equilibrium concentration of MII both by disordering acyl chain packing and by disrupting rhodopsin-water hydrogen bonds, demonstrating a direct effect of ethanol on rhodopsin. At physiologically relevant levels of osmolality and ethanol, about 90% of ethanol's effect is due to disordered acyl chain packing.

Animals↗
PubMed2000

Cholesterol dependent recruitment of di22:6-PC by a G protein-coupled receptor into lateral domains.

Bovine rhodopsin was reconstituted into mixtures of didocosahexaenoylphosphatidylcholine (di22:6-PC), dipalmitoylphosphatidylcholine (di16:0-PC), sn-1-palmitoyl-sn-2-docosahexaenoylphosphatidylcholine (16:0, 22:6-PC) and cholesterol. Rhodopsin denaturation was examined by using high-sensitivity differential scanning calorimetry. The unfolding temperature was increased at lower levels of lipid unsaturation, but the highest temperature was detected for native disk membranes: di22:6-PC < 16:0,22:6-PC < di16:0,18:1-PC < native disks. The incorporation of 30 mol% of cholesterol resulted in 2-4 degrees C increase of denaturation temperature in all reconstituted systems examined. From the analysis of van't Hoff's and calorimetric enthalpies, it was concluded that the presence of cholesterol in di22:6-PC-containing bilayers induces a level of cooperativity in rhodopsin unfolding. Fluorescence resonance energy transfer (FRET), using lipids labeled at the headgroup with pyrene (Py) as donors and rhodopsin retinal group as acceptor of fluorescence, was used to study rhodopsin association with lipids. Higher FRET efficiencies detected for di22:6-PE-Py, compared to di16:0-PE-Py, in mixed di22:6-PC-di16:0-PC-cholesterol bilayers, indicate preferential segregation of rhodopsin with polyunsaturated lipids. The effective range of the rhodopsin-lipid interactions facilitating cluster formation exceeds two adjacent lipid layers. In similar mixed bilayers containing no cholesterol, cluster formation was absent at temperatures above lipid phase transition, indicating a crucial role of cholesterol in microdomain formation.

Animals↗
PubMed2000

Measurement of dipolar couplings in a transducin peptide fragment weakly bound to oriented photo-activated rhodopsin.

Rhodopsin-containing disks, isolated from rod outer segments of bovine retina, align at high magnetic fields with their membrane normal parallel to the magnetic field. After light-activation of rhodopsin, transient binding of the C-terminal transducin undecapeptide, selectively labeled with 15N at Leu5 and Gly9, results in residual dipolar contributions to the 1J(NH) splittings for these two residues. Both residues show 1J(NH) splittings which are smaller than in the dark-adapted or rhodopsin-free sample, and return to their isotropic values at a rate determined by the decay of the meta II state of rhodopsin. The dipolar couplings indicate that in the bound state, N-H vectors of Leu5 and Gly9 make angles of 48+/-4 degrees and 40+/-8 degrees, respectively, with the disk normal. These 'transferred' dipolar couplings potentially offer a useful method for studying the conformation and orientation of flexible, low affinity ligands when bound to oriented integral membrane receptors.

Amino Acid Sequence↗
PubMed1999

Effect of protein hydration on receptor conformation: decreased levels of bound water promote metarhodopsin II formation.

Neutral solutes were used to investigate the effects of osmotic stress both on the ability of rhodopsin to undergo its activating conformation change and on acyl chain packing in the rod outer segment (ROS) disk membrane. The equilibrium concentration of metarhodopsin II (MII), the conformation of photoactivated rhodopsin, which binds and activates transducin, was increased by glycerol, sucrose, and stachyose in a manner which was linear with osmolality. Analysis of this shift in equilibrium in terms of the dependence of ln(Keq) on osmolality revealed that 20 +/- 1 water molecules are released during the MI-to-MII transition at 20 degrees C, and at 35 degrees C 13 +/- 1 waters are released. At 35 degrees C the average time constant for MII formation was increased from 1.20 +/- 0.09 ms to 1.63 +/- 0.09 ms by addition of 1 osmolal sucrose or glycerol. The effect of the neutral solutes on acyl chain packing in the ROS disk membrane was assessed via measurements of the fluorescence lifetime and anisotropy decay of 1,6-diphenyl-1,3,5-hexatriene (DPH). Analysis of the anisotropy decay of DPH in terms of the rotational diffusion model showed that the angular width of the equilibrium orientational distribution of DPH about the membrane normal was progressively narrowed by increased osmolality. The parameter fv, which is proportional to the overlap between the DPH orientational probability distribution and a random orientational distribution, was reduced by the osmolytes in a manner which was linear with osmolality. This study highlights the potentially opposing interplay between the effect of membrane surface hydration on both the lipid bilayer and integral membrane protein structure. Our results further demonstrate that the binding and release of water molecules play an important role in modulating functional conformational changes for integral membrane proteins, as well as for soluble globular proteins.

Animals↗
PubMed1998

Molecular order and dynamics in bilayers consisting of highly polyunsaturated phospholipids.

The time-resolved fluorescence emission and decay of fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) was used to characterize equilibrium and dynamic bilayer structural properties of symmetrically substituted phosphatidylcholines (PCs) with acyl chains containing no, one, four, or six double bonds and mixed-chain phosphatidylcholines with a saturated sn-1 chain and one, four, or six double bonds in the sn-2 chain. Both the Brownian rotational diffusion (BRD) model and the wobble-in-cone model were fit to all differential polarization data, and the descriptions of the data provided by the BRD model were found to be statistically superior. Global analysis of differential polarization data revealed two statistically equivalent solutions. The solution corresponding to a bimodal orientational distribution function, f(theta), was selected based on the effects of temperature on f(theta) and previous measurements on fixed, oriented bilayers. The overall equilibrium acyl chain order in these bilayers was analyzed by comparing the orientational probability distribution for DPH, f(theta) sin theta, with a random orientational distribution. Orientational order decreased and probe dynamics increased in mixed-chain species as the unsaturation of the sn-2 chain was increased. The degree of orientational order dropped dramatically in the dipolyunsaturated species compared with the mixed-chain phosphatidylcholines, which contained a polyunsaturated sn-2 chain. In terms of both orientational order and probe dynamics, the differences between the highly polyunsaturated species and the monounsaturated species were much greater than the differences between the monounsaturated species and a disaturated PC.

Diphenylhexatriene↗
PubMed1998

Effect of cholesterol on molecular order and dynamics in highly polyunsaturated phospholipid bilayers.

The effect of cholesterol on phospholipid acyl chain packing in bilayers consisting of highly unsaturated acyl chains in the liquid crystalline phase was examined for a series of symmetrically and asymmetrically substituted phosphatidylcholines (PCs). The time-resolved fluorescence emission and decay of fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) was used to characterize equilibrium and dynamic structural properties of bilayers containing 30 mol % cholesterol. The bilayers were composed of symmetrically substituted PCs with acyl chains of 14:0, 18:1n9, 20:4n6, or 22:6n3, containing 0, 1, 4, or 6 double bonds, respectively, and mixed-chain PCs with a saturated 16:0 sn-1 chain and 1, 4, or 6 double bonds in the sn-2 chain. DPH excited-state lifetime was fit to a Lorentzian lifetime distribution, the center of which was increased 1-2 ns by 30 mol % cholesterol relative to the cholesterol-free bilayers. Lifetime distributions were dramatically narrowed by the addition of cholesterol in all bilayers except the two consisting of dipolyunsaturated PCs. DPH anisotropy decay was interpreted in terms of the Brownian rotational diffusion model. The effect of cholesterol on both the perpendicular diffusion coefficient D perpendicular and the orientational distribution function f(theta) varied with acyl chain unsaturation. In all bilayers, except the two dipolyunsaturated PCs, 30 mol % cholesterol dramatically slowed DPH rotational motion and restricted DPH orientational freedom. The effect of cholesterol was especially diminished in di-22:6n3 PC, suggesting that this phospholipid may be particularly effective at promoting lateral domains, which are cholesterol-rich and unsaturation-rich, respectively. The results are discussed in terms of a model for lipid packing in membranes containing cholesterol and PCs with highly unsaturated acyl chains.

Cholesterol↗
PubMed1996

Primary alcohols modulate the activation of the G protein-coupled receptor rhodopsin by a lipid-mediated mechanism.

The visual pigment rhodopsin is a prototypical member of the G protein-coupled receptor superfamily. In this study, we have investigated the effect of a series of n-alcohols on the formation of metarhodopsin II (MII), the photoactivated conformation of rhodopsin, which binds and activates transducin. When rhodopsin was photolyzed in the presence of several n-alcohols, increased MII formation was observed in the order ethanol > butanol > hexanol, whereas longer chain n-alcohols inhibited MII formation with decanol > octanol. The magnitude of the stimulatory effects was greater in a more highly unsaturated phospholipid. Alcohols, which enhanced MII formation also increased phospholipid acyl chain packing free volume, while those that decreased this bilayer property inhibited MII formation. An apparent discontinuity in the effect of these alcohols results when their potency is calculated in terms of the total aqueous alcohol concentration. In sharp contrast, a continuous variation in their behavior is observed, when their potency is calculated in terms of the amount of alcohol partitioned in the membrane. Our findings strongly support a lipid-mediated mechanism of action for alcohols on rhodopsin and, by analogy, for other G protein-coupled receptors.

Alcohols↗
PubMed1996

A role for phospholipid polyunsaturation in modulating membrane protein function.

Visual transduction is one of the best characterized G protein--coupled signalling systems. In addition, about 50% of the disk membrane phospholipid acyl chains are 22:6n-3, making this system ideal for determining the role of polyunsaturation in modulating membrane-signalling systems. The extent of formation of metarhodopsin II (MII), the G protein--activating photointermediate of rhodopsin, was studied in phospholipid vesicles composed of a variety of phosphatidylcholines, differing in their acyl chain composition at the sn-2 position. The amount of MII formed increased progressively with the level of acyl chain unsaturation at the sn-2 position. The effect of added cholesterol was to reduce the amount of MII formed. The acyl chain packing free volume of the rhodopsin containing lipid vesicles was characterized by a fractional volume parameter fv derived from measurements of the time-resolved fluorescence anisotropy decay of the hydrophobic membrane probe 1,6-diphenyl-1,3,5-hexatriene. The relationship among sn-2 acyl chain unsaturation, cholesterol content, and MII formation is explained on the basis of variation in fv with bilayer lipid composition and a novel model for the packing of phospholipids containing polyenoic acyl chains, such as 22:6n-3.

Fats, Unsaturated↗
PubMed1994

Effect of ethanol on metarhodopsin II formation is potentiated by phospholipid polyunsaturation.

The role of phospholipids in modulating the effect of ethanol on membrane receptor activation was investigated by studying the extent of metarhodopsin II (MII) formation in vesicles formed POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and PDPC (1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine) and in native rod outer segment disk membranes as a function of ethanol concentration. The equilibrium concentration of MII, the G protein-activating form of photoactivated rhodopsin, was found to increase as a function of ethanol concentration in all three bilayers. Phospholipid composition had a marked effect on ethanol potency, with the presence of polyunsaturated phospholipid acyl chains increasing ethanol potency by 40%. The effects of ethanol on lipid acyl chain packing in POPC and PDPC were investigated using frequency domain anisotropy decay measurements of the fluorescent membrane probe 1,6-diphenyl-1,3,5-hexatriene. Enhanced formation of MII due to the presence of ethanol was correlated with the effects of ethanol on acyl chain packing properties. These findings support a phospholipid-mediated mechanism for the action of ethanol in modulating integral membrane receptor conformation.

Cell Membrane↗
PubMed1992

Effect of phosphorylation on receptor conformation: the metarhodopsin I in equilibrium with metarhodopsin II equilibrium in multiply phosphorylated rhodopsin.

The superfamily of membrane-bound receptors, which function in signal transduction by activating a guanine nucleotide binding protein or G-protein in response to agonist binding, shares a number of structural and mechanistic properties. Among these similarities is downregulation of functional activity via receptor phosphorylation. In this study, the effects of intermediate levels of phosphorylation (greater than or equal to 4 added phosphates per receptor molecule) on receptor conformational equilibria are examined by comparing the photochemical properties of phosphorylated and unphosphorylated rhodopsins which were incorporated separately into 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine vesicles. Postflash spectra reflecting the contributions of metarhodopsins I, II, and III (meta I, meta II, and meta III) were obtained from these samples. Deconvolution of appropriate difference spectra allowed a determination of the concentration of the photointermediates of interest. Meta II is the form of photolyzed rhodopsin which binds and activates the visual G-protein (Gt); thus, its relative abundance at equilibrium and temporal stability are important parameters in determining the efficiency of visual signal transduction. The effects of pH and temperature on the meta I in equilibrium with meta II equilibrium constant (Keq) and the rate of decay of meta II to meta III were examined for the reconstituted phosphorylated and unphosphorylated rhodopsin samples. Keq was essentially unaffected by phosphorylation when measured at pH 7.0 and 8.0 and 20 and 37 degrees C. The decay time (lifetime) of meta II----meta III had a value of approximately 4.7 min in both phosphorylated and unphosphorylated samples.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Role of sn-1-saturated,sn-2-polyunsaturated phospholipids in control of membrane receptor conformational equilibrium: effects of cholesterol and acyl chain unsaturation on the metarhodopsin I in equilibrium with metarhodopsin II equilibrium.

The effect of phospholipid bilayer acyl chain packing free volume on the equilibrium concentration of the form of photolyzed rhodopsin which initiates visual signal transduction, metarhodopsin II (meta II), is examined in reconstituted systems formed from the saturated phospholipid dimyristoylphosphatidylcholine (DMPC) and in the polyunsaturated phospholipid sn-1-palmitoyl-sn-2-arachidonoylphosphatidylcholine (PAPC) with and without 30 mol% cholesterol. The extent of meta II formation is determined from both flash photolysis measurements and rapidly acquired absorbance spectra. Equilibrium and dynamic properties of the lipid bilayer are characterized by the dynamic fluorescence properties of 1,6-diphenyl-1,3,5-hexatriene (DPH). DPH orientational properties are characterized by fv, a parameter which reflects the volume available for probe reorientation in the bilayer, relative to that available in an unhindered, isotropic environment [Straume, M., & Litman, B. J. (1987) Biochemistry 26, 5121-5126]. The metarhodopsin I in equilibrium with meta II equilibrium constant, Keq has a linear relationship with fv for rhodopsin in PAPC vesicles with and without cholesterol as well as for rhodopsin in DMPC vesicles, and these two correlation lines have different slopes. The correlations between Keq and fv in PAPC and DMPC systems are compared with a similar correlation in the native rod outer segment disk membrane and one reported previously in an egg phosphatidylcholine (egg PC) system [Mitchell, D. C., Straume, M., Miller, J. L., & Litman, B. J. (1990) Biochemistry 29, 9143-9149].(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Functional equivalence of metarhodopsin II and the Gt-activating form of photolyzed bovine rhodopsin.

Absorption of a photon by the visual pigment rhodopsin leads to the formation of an activated conformational state, denoted rho*, which is capable of activating the visual G-protein, Gt. The bleaching of rhodopsin can be resolved into a series of spectrally distinct photointermediates. Previous studies suggest that the photointermediate metarhodopsin II (meta II, lambda max of 380 nm) corresponds to the physiologically active form rho*. In the studies reported herein, spectral and enzymological data were analyzed and compared so as to evaluate the temporal correspondence between meta II and rho*. This information was obtained by direct observation of the meta II and rho* decay times in parallel experiments utilizing identical preparations of urea-stripped, bovine retinal rod outer segment disk membranes at pH 8.0, 20 degrees C. Postflash spectra were deconvolved to resolve the meta II absorbance at 380 nm, and a decay time for the loss of meta II of 8.2 min (SD = 0.5 min) was obtained from fitting these data to a single-exponential decay process. The diminishing ability of bleached rhodopsin to activate Gt was measured by monitoring the level of catalyzed exchange of Gt-bound GDP for a nonhydrolyzable GTP analogue. Analysis of the decrease in the initial velocity of nucleotide exchange, measured at various postflash incubation times, yielded a rho* decay time of 7.7 min (SD = 0.5 min) when analyzed as a single-exponential process. The similarity of these decay times provides direct evidence that meta II and rho* are present over the same time regime, and further supports the equivalence of these two forms of photoactivated rhodopsin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Packing characteristics of highly unsaturated bilayer lipids: Raman spectroscopic studies of multilamellar phosphatidylcholine dispersions.

The thermotropic properties and acyl chain packing characteristics of multilamellar dispersions of highly unsaturated lipids were examined by Raman spectroscopy. Bilayer assemblies were composed of POPC (1-palmitoyl-2-oleoylphosphatidylcholine), PAPC (1-palmitoyl-2-arachidonylphosphatidylcholine), and PDPC (1-palmitoyl-2-docosahexaenoylphosphatidylcholine), lipid systems possessing saturated sn-1 chains and unsaturated sn-2 chains with one, four, and six double bonds, respectively. Raman spectra were recorded in the acyl chain 2800-3100-cm-1 carbon-hydrogen (C-H) stretching and 1100-1200-cm-1 carbon-carbon (C-C) stretching mode regions, spectral intervals reflecting both the inter- and intrachain order/disorder properties of the various lipid dispersions. In order to obtain C-H stretching mode spectra relevant solely to the sn-1 chains of PAPC and PDPC, liquid-phase spectra of arachidonic and docosahexaenoic acid, respectively, were subtracted from the observed phospholipid spectra. The unsaturated sn-2 chains of PAPC and PDPC undergo minimal conformational reorganizations as the bilayers pass from the gel to liquid-crystalline phases. Phase transition temperatures, Tm, derived from statistically fitting the temperature-dependent Raman spectral data are approximately -2.5, -22.5, and -3 degrees C for POPC, PAPC, and PDPC, respectively. As the degree of unsaturation increases from POPC to PAPC and PDPC, the cooperativity of the phase transition, as measured by its breadth, decreases. Estimates of the transition widths from the temperature profiles are approximately 15 degrees C for PAPC and 20 degrees C for PDPC. The behavior of various Raman spectral parameters for the lipid gel phase reflects the formation of lateral microdomains, or clusters, whose packing properties maximize the van der Waals interactions between sn-1 chains.(ABSTRACT TRUNCATED AT 250 WORDS)

Crystallography↗
PubMed1991

Rhodopsin in dimyristoylphosphatidylcholine-reconstituted bilayers forms metarhodopsin II and activates Gt.

The photochemical intermediate metarhodopsin II (meta II; lambda max = 380 nm) is generally identified with rho*, the conformation of photolyzed rhodopsin which binds and activates the visual G-protein, Gt [Emeis, D., & Hoffman, K.P. (1981) FEBS Lett. 136, 201-207]. Purified bovine rhodopsin was incorporated into vesicles consisting of dimyristoylphosphatidylcholine (DMPC), and the rapid formation of a photochemical intermediate absorbing maximally at 380 nm was quantified via both flash photolysis and equilibrium spectral measurements. Kinetic and equilibrium spectral measurements performed above the Tm of DMPC showed that Gt, in the absence of GTP, enhances the production of the 380-nm-absorbing species while reducing the concentration of the 478-nm-absorbing species, metarhodopsin I (meta I), in a manner similar to that observed in the native rod outer segment disk membrane. This Gt-induced shift in the equilibrium concentration of photointermediates indicated that the species with an absorbance maximum at 380 nm was meta II. The presence of rho* in the DMPC bilayer was established via measurements of photolysis-induced exchange of tritiated GMPPNP, a nonhydrolyzable analogue of GTP, on Gt. Above Tm, the metarhodopsin equilibrium is strongly shifted toward meta I relative to the native rod outer segment disk membrane; however, at 37 degrees C, 40% of the photointermediates are in the form of meta II. The formation of meta II above Tm is slowed by a factor of ca. 2 relative to the disk membrane. Below Tm, the equilibrium is shifted still further toward meta I, and meta II forms ca. 7 times slower than in the disk membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗