Bovine Rod Outer Segment Membranes Research Articles

Enzyme-linked immunosorbent assay for quantitative determination of the visual pigment rhodopsin in total-eye extracts

A versatile, multispecies enzyme-linked immunosorbent assay for the rod visual pigment (rhod)opsin has been developed. For this quantitative inhibition assay a monospecific polyclonal antiserum is used which is elicited in rabbits against bovine rod outer-segment membranes. Detergent concentrations as high as 1.0% can be used in the assay with only a slight loss in sensitivity. The assay allows quantitative determination of the apoprotein opsin with a detection level of about 0.04 pmol per sample by using standards prepared by illumination of spectrophotometrically determined amounts of rhodopsin. The antiserum shows considerable cross-reactivity with opsin from several species (mouse, rat, quail, monkey and man). The high degree of monospecificity and cross-reactivity of the antiserum already allowed quantitation of opsin content in crude eye extracts of mouse, rat and quail with a sensitivity comparable to that of bovine opsin. Similar types of multispecies immunoassays for quantitation of highly conserved membrane proteins can be developed using the described approach, requiring only a monospecific antiserum elicited against an easily accessible species and crude tissue extracts both for coating and as a source of the inhibitory antigen.

The use of galactosyltransferase to probe nitrocellulose-immobilized glycoproteins for nonreducing terminal N-acetylglucosamine residues

We report the use of UDPgalactose: N-acetyl- d-glucosaminyl-glycopeptide 4-β- d-galactosyltransferase (EC 2.4.1.38), purified from bovine milk, to detect nonreducing terminal N-acetylglucosamine residues on glycoproteins immobilized on nitrocellulose by electrophoretic transfer from sodium dodecyl sulfate-polyacrylamide gels. Soluble galactosyltransferase incorporates radiolabeled galactose from the substrate UDP-[6- 3H]galactose into the appropriate immobilized acceptor with high specificity. Incorporation is proportional to substrate amount and is saturable with time. The kinetics of labeling are independent of substrate amount. Half-maximal incorporation occurs by 4 h and saturation occurs by 16 h. We have used galactosyltransferase as a probe (i) to verify the presence of nonreducing terminal N-acetylglucosamine residues in bovine rod outer segment membrane rhodopsin and in several glycoproteins in F9 murine teratocarcinoma cells and (ii) to detect previously reported endo-β- N-acetylglucosaminidase activity in a commercial preparation of endoglycosidase F.

Inhibition of bovine rod outer segment GTPase by Bordetella pertussis toxin.

Incubation of photolyzed bovine rod outer segment (ROS) membranes with pertussis toxin led to an inhibition of GTPase activity in an NAD-dependent reaction. In the presence of [32P]NAD, pertussis toxin catalyzed the [32P]ADP-ribosylation of a 39-kDa ROS protein and the 39-kDa alpha-subunit of transducin purified from ROS membranes. The decrease in GTPase activity was paralleled by an increase in the extent of [32P]ADP-ribosylation of the 39-kDa ROS protein. [32P]ADP-ribosylation of the 39-kDa protein occurred in both photolyzed and dark ROS membranes. Neither ATP nor guanylyl imidodiphosphate were required for either ADP-ribosylation or inhibition of GTPase. It was demonstrated previously that choleragen catalyzed the NAD-dependent inhibition of ROS GTPase (Abood, M. E., Hurley, J. B., Pappone, M-C., Bourne, H. R., and Stryer, L. (1982) J. Biol. Chem. 257, 10540-10543). Choleragen-catalyzed inhibition of GTPase and [32P]ADP-ribosylation of the 39-kDa protein required guanylyl imidodiphosphate and did not occur in dark ROS membranes. The effects of choleragen and pertussis toxin were not additive. Incubation of ROS with choleragen or pertussis toxin prevented the subsequent [32P]ADP-ribosylation by the homologous but not the heterologous toxin, consistent with the hypothesis that the two toxins act at different sites on the 39-kDa protein. Pertussis toxin is known to ADP-ribosylate the inhibitory guanine nucleotide-binding subunit of adenylate cyclase (Ni) but not the stimulatory subunit (Ns); choleragen is known to ADP-ribosylate Ns but not Ni. Since both toxins ADP-ribosylate the same subunit of transducin, it appears that this protein may possess characteristics of both Ns and Ni.

A radioimmunoassay specific for opsin

A radioimmunoassay is developed for bovine opsin using a rabbit antiserum against bovine rod outer segment membranes. The assay is specific for opsin. Rhodopsin, bacteriorhodopsin and hemoglobin do not show cross-reaction. It can be carried out rapidly, has a sensitivity of 0.01 pmol bovine opsin and gives accurate results, even in the presence of a large excess of rhodopsin. Under the conditions described, the assay can be used to measure bovine opsin and rhodopsin in each other's presence by running a sample before and after illumination, with a sensitivity 2000-times higher than with spectrophotometric methods. The opsin content of rather crude preparations such as bovine retina homogenates can be accurately determined. Rabbit and mouse opsin can also be assayed with a reasonable degree of accuracy using the same rabbit antiserum.

Neuraminidase in Calf Retinal Outer Segment Membranes

An enzyme catalyzing the hydrolysis of sialic acid (N-acetylneuraminic acid: NeuNAc)-containing glycoconjugates has been found in bovine retinal rod outer segment (ROS) membranes. The enzymatic activity is optimal at pH 4.0 and is stimulated by 0.15% Triton X-100. Total activity was determined by the release of NeuNac from endogenous and exogenous substrates (GD1a). The ROS enzyme preferentially hydrolyses the ROS gangliosides, possibly because they are more accessible than the glycoproteins as substrates for the neuraminidase. Release of NeuNAc from gangliosides leads to important changes in the ganglioside patterns; whereas the amounts of GM1 increased throughout the incubation, the levels of polysialogangliosides GT1b and GD3 diminished owing to their rapid hydrolysis. The finding that gangliosides are hydrolysed more extensively than glycoproteins suggests that endogenous ROS gangliosides may be the principal source of metabolically available sialic acid in ROS. It was also observed that the activity of ROS neuraminidase is not affected by illumination of the membranes.

X-ray diffraction and electron microscope study of phase separation in rod outer segment photoreceptor membrane multilayers

Phase separation in artificially stacked multilayers of isolated bovine retinal rod outer segment (ROS) membranes has been examined via x-ray diffraction and electron microscopy. Specimens were prepared by isopotential spin drying followed with partial hydration by equilibration against moist gas streams. Upon dehydration, the multilamellar membrane phase assumes a binary phase composition consisting of concentrated protein-containing lamellae interspersed with microdomains of hexagonally packed tubes of lipid in a HII configuration. The HII lattice is geometrically coupled to the lamellar phase with one set of hexagonal crystal planes co-planar to the local membrane lamellae. The hexagonal microdomains bear a striking resemblance to the "paracrystalline inclusions" observed in fast-frozen, intact frog ROS (Corless and Costello. 1981. Exp. Eye Res. 32:217). The lamellar lattice is characterized by an unusually small degree of disorder. Sharp lamellar diffraction with a 120 A unit cell is observed (at near total dehydration) to a resolution of 6 A. A model consistent with the data is that a multilamellar array of ROS disks is stable as long as the external disk surfaces are kept sufficiently far apart. If the distance between the membranes is allowed to shrink below a certain critical value, the disk lipids spontaneously convert to a nonbilayer phase. This suggests that the structure of the ROS is stabilized by an internal framework that acts to keep the disks apart from one another and from the plasmalemma. Thus, the necessity of avoiding phase separations may provide a rationale for the peculiar morphology of the ROS.

Sterol composition of bovine retinal rod outer segment membranes and whole retinas

The sterol composition of bovine retinal rod outer segment membranes and whole retinas was studied by detailed chromatographic analyses. Cholesterol represented at least 98% of the total 3 β-monohydroxy sterols of rod outer segment membranes, accounting for 1.68 ± 0.15% of the dry weight. Whole retinas contained 1.76 ± 0.29% cholesterol by dry weight, representing at least 99% of the total 3β-monohydroxy sterols. Trace amounts of a component having the chromatographic properties of 5α-cholestan-3β-ol were found in rod outer segment membranes and whole retinas. Very small amounts of a component having the chromatographie properties of 5α-cholest-7-en-3β-ol were found in whole retinas, but not in rod outer segment membranes. The molar ratio of cholesterol to rhodopsin in bovine rod outer segment membranes was approximately 4.7. Cholesterol accounted for only 5–7 mol% of total rod outer segment membrane lipids.

Light-induced interactions between rhodopsin and the GTP-binding protein. Relation with phosphodiesterase activation.

The existence of rapid light-induced changes of light scattering in suspensions of bovine rod outer segment membranes has been described previously [H. Kühn et al. (1981) Proc. Natl Acad. Sci. USA, 78, 6873-6877]. The signal observed in the presence of GTP has been interpreted as being related to the rhodopsin-catalyzed exchange of GTP for GDP bound to the GTP-binding protein, i.e. to the formation of the activator of the cGMP phosphodiesterase [B.K.K. Fung et al. (1981) Proc. Natl Acad. Sci. USA, 78, 152-156]. We have tested this interpretation in the present paper by investigating the relation between the light-scattering signal and the activity of the phosphodiesterase using rapid recording techniques for both processes. All the results obtained are consistent with the above hypothesis. The amplitude of the light-scattering signal and the activity of the phosphodiesterase are shown to present the same dependence upon the flash intensity and upon the concentration of GTP or its analog guanosine 5'-[beta, gamma--imido]triphosphate (p[NH]ppG). The results suggest that the GTP-binding protein possesses one high-affinity p[NH]ppG-binding site (Kd much less than 0.1 microM). At high concentrations of GTP or p[NH]ppG the phosphodiesterase is activated in the dark and the light-scattering signal is correspondingly reduced; both effects are prevented by previous incubation with guanosine 5'-[beta-thio]diphosphate (p[S]pG).

66] Preparation of bovine rod outer segment membranes capable of regenerating visual pigment with added 11-cis-retinol

Publisher Summary This chapter illustrates the preparation of bovine rod outer segment membranes capable of regenerating visual pigment with added 11- cis -retinol. Bovine rod outer segment membranes (ROSM) isolated by sucrose density gradient centrifugation are unable to regenerate visual pigment with added 11- cis -retinol. The procedure to be described provides an alternative means of isolating ROSM utilizing glycerol and ethylene glycol. It yields an impure preparation with an active nicotinamide adenine dinucleotide (NAD + )-dependent 11- cis -retinol dehydrogenase capable of regenerating visual pigment with added 11- cis -retinol and NAD + . The entire procedure takes at least 14 hr but could be substantially shortened by use of fresh retina. As such it is usually carded out in two successive days. All work is done under dim red light or the dark at 4 °.

ESR spin-label studies of lipid-protein interactions in membranes

Lipid spin labels have been used to study lipid-protein interactions in bovine and frog rod outer segment disc membranes, in (Na+, K+)-ATPase membranes from shark rectal gland, and in yeast cytochrome oxidase-dimyristoyl phosphatidylcholine complexes. These systems all display a two component ESR spectrum from 14-doxyl lipid spin-labels. One component corresponds to the normal fluid bilayer lipids. The second component has a greater degree of motional restriction and arises from lipids interacting with the protein. For the phosphatidylcholine spin label there are effectively 55 +/- 5 lipids/200,000-dalton cytochrome oxidase, 58 +/- 4 mol lipid/265,000 dalton (Na+, K+)-ATPase, and 24 +/- 3 and 22 +/- 2 mol lipid/37,000 dalton rhodopsin for the bovine and frog preparations, respectively. These values correlate roughly with the intramembrane protein perimeter and scale with the square root of the molecular weight of the protein. For cytochrome oxidase the motionally restricted component bears a fixed stoichiometry to the protein at high lipid:protein ratios, and is reduced at low lipid:protein ratios to an extent which can be quantitatively accounted for by random protein-protein contacts. Experiments with spin labels of different headgroups indicate a marked selectivity of cytochrome oxidase and the (Na+, K+)-ATPase for stearic acid and for cardiolipin, relative to phosphatidylcholine. The motionally restricted component from the cardiolipin spin label is 80% greater than from the phosphatidylcholine spin label for cytochrome oxidase (at lipid:protein = 90.1), and 160% greater for the (Na+, K+)-ATPase. The corresponding increases for the stearic acid label are 20% for cytochrome oxidase and 40% for (Na+, K+)-ATPase. The effective association constant for cardiolipin is approximately 4.5 times greater than for phosphatidylcholine, and that for stearic acid is 1.5 times greater, in both systems. Almost no specificity is found in the interaction of spin-labeled lipids (including cardiolipin) with rhodopsin in the rod outer segment disc membrane. The linewidths of the fluid spin-label component in bovine rod outer segment membranes are consistently higher than those in bilayers of the extracted membrane lipids and provide valuable information on the rate of exchange between the two lipid components, which is suggested to be in the range of 10(6)-10(7) s-1.

Interactions between photoexcited rhodopsin and GTP-binding protein: kinetic and stoichiometric analyses from light-scattering changes.

In rod outer segments, photoexcited rhodopsin (R*) activates a cyclic GMP phosphodiesterase through a sequence of reactions involving a GTP-binding protein. By measuring light-scattering changes above 700 nm, we have studied the kinetics and stoichiometry of the association of R* with this protein and of the dissociation of the complex upon GDP/GTP exchange. Two light-scattering signals were obtained upon photoexcitation of rhodopsin in bovine rod outer segment membranes as well as in a reconstituted system consisting of purified GTP-binding protein and washed disc membranes; both signals depended specifically on the presence of GTP-binding protein. A "binding signal" that was observed in the absence of gTP as an increase in turbidity became saturated when a number of rhodopsin molecules equal to the number of GTP-binding protein molecules present (congruent to 10% in rod outer segments) has been bleached, suggesting that the protein binds to R* in a 1:1 complex. A "dissociation signal" of opposite sign, observed in presence of GTP at greater than or equal to 1 microM, is half maximal at 0.04% bleaching and saturated at 0.5% bleaching; it is interpreted as reflecting the dissociation of GTP-binding protein-R* complexes after GDP/GTP exchange on the GTP-binding protein, one R* being able to interact sequentially with about 100 GTP-binding protein molecules. The early time course of the binding signal is faster than that of the dissociation signal, and both signals take place in the 100-msec range at 20 degrees C.

Distinct states of lipid mobility in bovine rod outer segment membranes Resolution of spin label results

Freely diffusable lipid spin labels in bovine rod outer segment disc membranes display an apparent two-component ESR spectrum. One component is markedly more immobilized than that found in fluid lipid bilayers, and is attributed to lipid interacting directly with rhodopsin. For the 14-doxyl stearic acid spin label this more immobilized component has an outer splitting of 59 G at 0°C, with a considerable temperature dependence, the effective outer splitting decreasing to 54 G at 24°C. Spin label lipid chains covalently attached to rhodopsin can also display a two-component spectrum in rod outer segment membranes. In unbleached, non-delipidated membranes the 16-doxyl stearoyl maleimide label shows an immobilized component which has an outer splitting of 59 G at 0°C and a considerable temperature dependence. This component which is not resolved at high temperatures (24–35°C), is attributed to the lipid chains interacting directly with the monomeric protein, as with the diffusable labels. In contrast, in rod outer segment membranes which have been either delipidated or extensively bleached, a strongly immobilized component is observed with the 16-doxyl maleimide label at all temperatures. This immobilized component has an outer splitting of 62–64 G at 0°C, with very little temperature dependence (61–62 G at 35°C), and is attributed to protein aggregation.

The involvement of water at the retinal binding site in rhodopsin and early light-induced intramolecular proton transfer.

Abstract Extensive dehydration of air‐dried films of bovine rod outer segment membranes induces fully reversible changes in the absorption spectrum of rhodopsin, indicative of deprotonation of the retinylidene Schiff base in more than 50% of the rhodopsin molecules in the sample. This suggests that water is involved at the site of the Schiff base protonation in rhodopsin. In contrast, the spectrum of metarhodopsin I is resistant to similar dehydrating conditions, implying a significant difference in the mechanism for protonation in metarhodopsin I. The photochemistry of dehydrated membranes was also explored. Photoexcitation of deprotonated rhodopsin (λmax 390 nm) induces a large bathochromic shift of the chromophore. The major photoproduct at room temperature was spectrally similar to metarhodopsin I (λmax, 478 nm). These findings suggest that intramolecular proton transfer involving the Schiff base proton may occur in the earlier stages of the visual cycle, prior to or during the formation of metarhodopsin I.

Rhodopsin photoenergetics: lumirhodopsin and the complete energy profile

1. Introduction Various intermediate stages in the photolysis of visual pigments have been recognised, but neither their stereochemical form nor their relation to the actual process of visual excitation have been resolved (review [I]). The relative energies of many of the intermedi- ates in the bovine rhodopsin bleaching sequence have been determined in recent years by direct photocalo- rimetric methods [2-I]. Here I report the measure- ment of the enthalpy change associated with the light- induced formation of lumirhodopsin in bovine photo- receptor membranes at -75°C. This completes the sequence of calorimetrically accessible intermediates, and allows construction of an energy profile for the entire process which establishes firm thermodynamic constraints for proposed molecular mechanisms. 2. Materials and methods Bovine rod outer segment membranes (ROS) were prepared by a standard sucrose density gradient tech- nique [5] from the retinas of fresh, dark-adapted cattle eyes, obtained locally. Samples for photocalo- rimetry were prepared by suspension of ROS in a mixture of glycerol (2 vol.) and 0.1 M sodium phos- phate buffer (1 vol.), pH 7.2 at room temperature. Rhodopsin concentrations and the extent of bleaching during calorimetry were determined from room tem- perature absorbance spectra of aliquots of the ROS suspension dispersed in 2% (w/v) CTAB (cetyltrimeth- ylammonium bromide, Sigma Chem. Co.), 0.1 M phosphate buffer, pH 7 .?I, containing 10 mM hydrox- ylamine hydrochloride, assuming a molar extinction coefficient of 41 000 at 500 nm. Unless otherwise stated, all operations were performed in the dark or under dim red light. 324 Instrumental details of the low-temperature photo- calorimeter have appeared in [3,6]. For these experi- ments the entire calorimetric unit was surrounded by a copper circulation coil and suspended in a Dewar vessel filled with methanol. The system was further insulated with expanded polystyrene foam and mounted in a temperature-controlled ( 20 f 1°C) darkroom. The calorimeter was cooled to -75°C by circulation of methanol from a low-temperature bath, modified for proportional temperature control with a Pt resistance probe and precision electronic controller. Sample illumination was via glass fibre optics from a grating monochromator and a stabilised 200 W xenon arc lamp. Electrical calibration gave an instrumental sensitivity of 0.071 pV/pW under these conditions. The amplified signal, integrated over 60 s intervals, was recorded digitally as a function of time through- out an experiment. In a typical experiment the photocalorimeter was loaded with 2 .O ml ROS suspension (Esoo = 1) together with a reference sample of the same material totally bleached at room temperature prior to loading. After thermal equilibration at -75°C for several hours (usually overnight) the sample was irradiated briefly at 480 or 520 nm and the differential thermal response recorded. The sample was then removed, warmed to room temperature, and an aliquot taken for spectral determination of the amount of photoreaction in comparison with starting material. Control experi- ments included trials with bleached material in both calorimeter cells. 3. Results and discussion Lumirhodopsin is the kinetically stable photo- product of bovine rhodopsin at -75°C and the reac- tion only proceeds to subsequent stages on warming

Light-enhanced cross-linking of rhodopsin in rod outer segment membranes as detected by chemical probes

Bovine rod outer segment membranes were treated with cross-linking reagents before and after light exposure. Bleached membranes showed enhanced cross-linking with difluorodinitrobenzene or methyl acetimidate compared to dark-adapted membranes. The light-induced enhancement of cross-linking may be due to increased association of rhodopsin monomers in the light and/or due to increased reactivity of amino and sulfhydryl groups of bleached rhodopsin. In some instances, the band ascribed to the rhodopsin monomer in gel electrophoresis appears as a partially resolved doublet. Treatment of bleached rod outer segment membranes with methyl acetimidate improved the resolution of the doublet into two closely migrating bands.

Tryptophan in bovine rhodopsin: its content, spectral properties and environment.

The tryptophan content of purified bovine rhodopsin was obtained by two independent methods: direct analysis of hydrolysates prepared by digestion of opsin with methanesulfonic acid containing 0.2% 3-(2-aminoethyl)indole and a computer-assisted analysis of the near-UV spectrum of rhodopsin. Both methods gave a value of eight tryptophan residues per rhodopsin. Based on the near-UV spectral analysis, the light-induced difference spectrum of rhodopsin, and the susceptibility of residues to oxidation by N-bromosuccinimide, we concluded that approximately half of the tyrosine and tryptophan residues are shielded to some extent from the aqueous solvent, that two of the tryptophan residues are in very apolar environments, and that following light excitation at least one of these tryptophan residues and several tyrosines are exposed to an aqueous environment. Analysis of rhodopsin absorption in the far-UV indicated that below 240 nm, approximately half of the absorption is due to aromatic residues and that the other half is largely due to the peptide bond. The effect of illumination on secondary structure is to induce a loss in helical structure, calculated to involve 35% of the amino acid residues in purified rhodopsin. If light-induced changes in secondary structure are specifically excluded, most of these results can be extended to bovine rod outer segment membranes.

The disk membrane as model for an excitable membrane

Excitable membranes appear to be biochemically characterized by the presence of a highly specific receptor protein, which undergoes conformational changes upon stimulation and returns to its original conformation for renewed excitability. Our present knowledge of the disk membrane and its receptor protein rhodopsin is reviewed in the light of this model. The influence of the membrane environment on rhodopsin has been determined in bovine rod outer segment membranes, in rhodopsin preparations which are depleted of the membrane phospholipids, and in reconstituted phospholipid-rhodopsin vesicles. Except for the absorbance spectrum in the visual region, all properties studied change upon lipid depletion. This process starts when 30% of the phospholipids have been removed. Upon reincorporation of lipid-free rhodopsin into lipid bilayer membranes, all properties are restored to the values observed in the native membranes. Hence, removal of the membrane causes deficiencies in the rhodopsin molecule, which are reversible under appropriate conditions. With respect to the function of rhodopsin in visual excitation, the photolytic sequence seems to be the most relevant parameter presently available. Experimental evidence indicates a partial unfolding of the protein upon illumination, culminating at the metarhodopsin I to II transition, followed by a refolding, which is largely completed in the free opsin stage. While the unfolding phase of the photolytic process apparently is independent of the microenvironment of the rhodopsin molecule, the refolding phase seems to require embedding in a partially hydrophobic environment which allows sufficient thermal motion, e.g. a semifluid biomembrane.

Rhodopsin-lipid associations in bovine rod outer segment membranes. Identification of immobilized lipid by spin-labels

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRhodopsin-lipid associations in bovine rod outer segment membranes. Identification of immobilized lipid by spin-labelsAnthony Watts, Igor D. Volotovski, and Derek MarshCite this: Biochemistry 1979, 18, 22, 5006–5013Publication Date (Print):October 1, 1979Publication History Published online1 May 2002Published inissue 1 October 1979https://doi.org/10.1021/bi00589a031RIGHTS & PERMISSIONSArticle Views115Altmetric-Citations135LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (970 KB) Get e-Alerts Get e-Alerts

Biochemical aspects of the visual process XL. Spectral and chemical analysis of metarhodopsin III in photoreceptor membrane suspensions

The late photointermediates of rhodopsin photolysis have been analyzed spectrally and chemically in bovine rod outer segment membrane suspension at 25°C and pH 6.5. The decay of metarhodopsin II follows two spectrally distinct routes, resulting 40 min after illumination in a stable mixture of photoproducts with absorbance maxima around 380 and 452 nm, free retinal and metarhodopsin III, respectively. Chemical analysis shows that three different products are involved: free retinal (approx. 34%), protein-bound retinal (approx. 51%) and lipid-bound retinal (approx. 15%). The latter fraction consists of retinylidene-phosphatidylethanolamine exclusively. Photolysis of membranes reconstituted with various phospholipids gives a qualitatively normal spectral picture, but the production of metarhodopsin III may vary with the phospholipid composition, i.e. with the percent of phosphatidylethanolamine present. Chemical analysis shows that with increasing phosphatidylethanolamine content of the membrane, the retinylidene phosphatidylethanolamine fraction increases proportionally at the expense of free retinal, while the fraction of protein-bound retinal remains unaffected. The results indicate that under these conditions metarhodopsin III (defined as a long wavelength product of metahrodopsin II decay) is composed of two chemically distinct components: opsin-bound retinal and retinylidene phosphatidylethanolamine.

A comparison of the effects of calcium on the structure of bovine retinal rod outer segment membranes, phospholipids, and bovine brain phosphatidylserine.

A comparison of the effects of calcium on the structure of bovine retinal rod outer segment membranes, phospholipids, and bovine brain phosphatidylserine.