Euphausiid visual pigments. The rhodopsins of Euphausia superba and Meganyctiphanes norvegica (Crustacea, Euphausiacea)

The rhabdoms of Euphausia superba contain one digitonin-extractable rhodopsin, lambda max 485 nm. The rhodopsin undergoes unusual pH- dependent spectral changes: above neutrality, the absorbance decreases progressively at 485 nm and rises near 370 nm. This change is reversible and appears to reflect an equilibrium between a protonated and an unprotonated form of the rhodopsin Schiff-base linkage. Near neutral pH and at 10 degrees C, the rhodopsin is partiaLly converted by 420-nm light to a stable 493-nm metarhodopsin. The metarhodopsin is partially photoconverted to rhodopsin by long-wavelength light in the absence of NH2OH; in the presence of NH2OH, it is slowly converted to retinal oxime and opsin. The rhodopsin of Meganyctiphanes norvegica measured in fresh rhabdoms by microspectrophotometry has properties very similar to those of the extracted rhodopsin of E. superba. Its lambda max is 488 nm and it is partially photoconverted by short wavelength irradiation to a stable photoconvertible metarhodopsin similar to that of E. superba. In the presence of light and NH2OH, the M. norvegica metarhodopsin is converted to retinal oxime and opsin. Our results indicate that previous determinations of euphausiid rhodopsin absorbance spectra were incorrect because of accessory pigment contamination.     

Photoregeneration of visual pigments in a moth

Summary The spectral absorbance by the visual pigments in the compound eye of the mothDeilephila elpenor was determined by microphotometry. Two visual pigments and their photoproducts were demonstrated. The photoproducts are thermostable and are reconverted to the visual pigments by light. The concentrations of the visual pigments and the photoproducts at each wavelength are determined by their absorbance coefficients at this wavelength. P 525: The experimental recordings (difference spectra and spectral absorbance changes after exposure to monochromatic lights) were completely reproduced by calculations using nomograms for vertebrate rhodopsin. The identity between experimental recordings and calculations show: One visual pigment absorbs maximally at 525 nm (P 525). The resonance spectrum of the visual pigment is identical to that for a vertebrate rhodopsin (_max at 525 nm). The photoproduct of this pigment absorbs maximally at 480 nm (M 480). It is similar to the acid metarhodopsin in cephalopods. The relative absorbance of P 525 to that of M 480 is 11.75. The quantum efficiency for photoconversion of P 525 to M 480 is nearly equal to that for reconversion of M 480 to P 525. Wavelengths exceeding about 570 nm are absorbed only by P 525, i. e. P 525 is completely converted to M 480. Shorter wavelengths are absorbed both by P 525 and M 480. At these wavelengths a photoequilibrium between the two pigments is formed. Maximal concentration of P 525 is obtained at about 450 nm. P 350: A second visual pigment absorbs maximally at about 350 nm (P 350), and its photoproduct at 450 to 460 nm. In the region of spectral overlap a photoequilibrium between the two pigments is formed.The visual pigment and the photoproduct are similar to those in the neuropteran insectAscalaphus.The work reported in this article was supported by Deutsche Forschungsgemeinschaft, Schwerpunktsprogramm Rezeptorphysiologie Ha 258-10, and SFB 114, by the Swedish Medical Research Council (grant no B 73-04X-104-02B), by Karolinska Institutet, and by a grant (to G. Höglund) from Deutscher Akademischer Austauschdienst.     

Studies on cephalopod rhodopsin. Conformational changes in chromophore and protein during the photoregeneration process

The ultraviolet absorbance of squid and octopus rhodopsin changes reversibly at 234 nm and near 280 nm in the interconversion of rhodopsin and metarhodopsin. The absorbance change near 280 nm is ascribed to both protein and chromophore parts. Rhodopsin is photoregenerated from metarhodopsin via an intermediate, P380, on irradiation with yellow light (λ > 520 nm). The ultraviolet absorbance decreases in the change from rhodopsin to metarhodopsin and recovers in two steps; mostly in the process from metarhodopsin to P380 and to a lesser extent in the process from P380 to rhodopsin. P380 has a circular dichroism (CD) band at 380 nm and its magnitude is the same order as that of rhodopsin. Thus it is considered that the molecular structure of P380 is close to that of rhodopsin and that the chromophore is fixed to opsin as in rhodopsin. In the change from metarhodopsin to P380, the chromophore is isomerized from the all-trans to the 11-cis form, and the conformation of opsin changes to fit 11-cis retinal. In the change from P380 to rhodopsin, a small change in the conformation of the protein part and the protonation of the Schiff base, the primary retinal-opsin link, occur.     

Genetic analyses of visual pigments of the pigeon (Columba livia)

We isolated five classes of retinal opsin genes rh1(Cl), rh2(Cl), sws1(Cl), sws2(Cl), and lws(Cl) from the pigeon; these encode RH1(Cl), RH2(Cl), SWS1(Cl), SWS2(Cl), and LWS(Cl) opsins, respectively. Upon binding to 11-cis-retinal, these opsins regenerate the corresponding photosensitive molecules, visual pigments. The absorbance spectra of visual pigments have a broad bell shape with the peak, being called lambdamax. Previously, the SWS1(Cl) opsin cDNA was isolated from the pigeon retinal RNA, expressed in cultured COS1 cells, reconstituted with 11-cis-retinal, and the lambdamax of the resulting SWS1(Cl) pigment was shown to be 393 nm. In this article, using the same methods, the lambdamax values of RH1(Cl), RH2(Cl), SWS2(Cl), and LWS(Cl) pigments were determined to be 502, 503, 448, and 559 nm, respectively. The pigeon is also known for its UV vision, detecting light at 320-380 nm. Being the only pigments that absorb light below 400 nm, the SWS1(Cl) pigments must mediate its UV vision. We also determined that a nonretinal P(Cl) pigment in the pineal gland of the pigeon has a lambdamax value at 481 nm.     

Formation, conversion, and utilization of isorhodopsin, rhodopsin, and porphyropsin by rod photoreceptors in the Xenopus retina

The visual pigment content of rod photoreceptors in Xenopus larvae was reduced greater than 90% through a combination of vitamin A-deficient diet and constant light. Thereafter, a dose of either all-trans-retinol or 9-cis-retinal was injected intramuscularly, leading to the formation of a rhodopsin (lambdamax 504 nm) or isorhodopsin (lambdamax 487-493 nm) pigment, respectively. Electrophysiological measurements were made of the threshold and spectral sensitivity of the aspartate-isolated PIII (photoreceptoral) component of the electroretinogram. These measures established that either rhodopsin or isorhodopsin subserved visual transduction with the same efficiency as the 519 nm porphyropsin pigment encountered normally. When animals with rhodopsin or isorhodopsin were kept in darkness or placed on a cyclical lighting regimen for 8 days, retinal densitometry showed that either pigment was being converted to porphyropsin; significantly more porphyropsin was formed as a result of cyclical lighting than after complete darkness.     

Studies on cephalopod rhodopsin: photoisomerization of the chromophore.

Photoisomerization of the chromophore of squid rhodopsin is dependent upon the irradiation temperature. Above 0 degrees C, only 11-cis in equilibrium all-trans reaction proceeds and the all-trans leads to 9-cis reaction is limited to extremely low efficiency. At liquid nitrogen temperature, 11 cis in equilibrium all-trans in equilibrium 9-cis reaction takes place. At intermediary low temperatures (-80 degrees C to -15 degrees C) another isomer of retinal may be produced by the irradiation, which forms a pigment having an absorbance maximum at 465 nm (P-465). The formation of P-465 decreases remarkably in the narrow temperature range from -30 degrees C to 0 degrees C where mesorhodopsin converts to metarhodopsin. Medsorhodopsin is quite different from metarhodopsin in the photoisomerization of the chromophore because P-465 is produced from the former but not from the latter. No P-465 is produced both at liquid nitrogen temperature and above 0 degrees C. P-465 is more labile than any of the other photoproducts so far known, that is isorhodopsin, alkaline and acid metarhodopsins. P-465 is converted to metarhodopsin by irradiation.     

Octopus photoreceptor membranes. Surface charge density and pK of the Schiff base of the pigments.

The chromophore of octopus rhodopsin is 11-cis retinal, linked via a protonated Schiff base to the protein backbone. Its stable photoproduct, metarhodopsin, has all-trans retinal as its chromphore. The Schiff base of acid metarhodopsin (lambda max = 510 nm) is protonated, whereas that of alkaline metarhodopsin (lambda max = 376 nm) is unprotonated. Metarhodopsin in photoreceptor membranes was titrated and the apparent pK of the Schiff base was measured at different ionic strengths. From these salt-dependent pKs the surface charge density of the octopus photoreceptor membranes and the intrinsic Schiff base pK of metarhodopsin were obtained. The surface charge density is sigma = -1.6 +/- 0.1 electronic charges per 1,000 A2. Comparison of the measured surface charge density with values from octopus rhodopsin model structures suggests that the measured value is for the extracellular surface and so the Schiff base in metarhodopsin is freely accessible to protons from the extracellular side of the membrane. The intrinsic Schiff base pK of metarhodopsin is 8.44 +/- 0.12, whereas that of rhodopsin is found to be 10.65 +/- 0.10 in 4.0 M KCl. These pK values are significantly higher than the pK value around 7.0 for a retinal Schiff base in a polar solvent; we suggest that a plausible mechanism to increase the pK of the retinal pigments is the preorganization of their chromophore-binding sites. The preorganized site stabilizes the protonated Schiff base with respect to the unprotonated one. The difference in the pK for the octopus rhodopsin compared with metarhodopsin is attributed to the relative freedom of the latter's chromophore-binding site to rearrange itself after deprotonation of the Schiff base.     

Physiology and in situ identification of putative aminergic neurotransmitters in the nervous system of Gyrocotyle fimbriata, a parasitic flatworm

The longitudinal nerve cords (LNC) in Gyrocotyle fimbriata do not change their activity in response to catecholamines but are excited by the amino acids glutamate and aspartate at concentrations less than 10(-5)M. This activity can be blocked by application of 2-amino-4-phosphonobutyrate (APB), an aminergic blocking agent. In situ measurements of fluorescent spectra from LNC neurites have a lambdamax at 513.6 nm. Treatment with HCI shifts the peak to 510 nm. Both glutamate and aspartate fluoresce and behave similarly with peak emissions of 512.5 nm before HCI treatment and 511 nm and 509 nm, respectively, after treatment. Dopamine and norepinephrine both fluoresce at 512.2 nm but the peaks shifts to 516.5 and 528, respectively, following acid treatment. These experiments indicate that the fluorescing substance in the neurones is not a known catecholamine and could be an amino acid.     

The ultrastructure of the uterine epithelium of the pig during the estrous cycle and early pregnancy

Summary In the compound eye of the moth Antheraea polyphemus, three types of visual pigments were found in extracts from the retina and by microspectrophotometry in situ. The absorption maxima of the receptor pigment P and the metarhodopsin M are at (1) P 520–530 nm, M 480–490 nm; (2) P 460–480 nm, M 530–540 nm; (3) P 330–340 nm, M 460–470 nm. Their localization was investigated by electron microscopy on eyes illuminated with different monochromatic lights. Within the tiered rhabdom, constituted of the rhabdomeres of nine visual cells, the basal cell contains a blue-and the six medial cells have a greenabsorbing pigment. The two distal cells of most ommatidia also have the blue pigment; only in the dorsal region of the eye, these cells contain a UV-absorbing pigment, which constitutes a portion of only 5% of the visual pigment content within the entire retina. The functional significance of this distribution is discussed.     

Analysis of the rhodopsin cycle in limulus ventral photoreceptors using the early receptor potential

The early receptor potential (ERP) was recorded intracellularly from Limulus ventral photoreceptors. The ERP in cells dissected under red light was altered by exhaustive illumination. No recovery to the original wafeform was observed, even after 1 h in the dark. The ERP waveform could be further altered by chromatic adaptation or by changes in pH. The results indicate that at pH 7.8 there are two interconvertible pigment states with only slightly different lambdamax, whereas at pH 9.6 there are two interconvertible states with very different lambdamax. Under all conditions studied the ERPs were almost identical with those previously obtained in squid retinas. This strongly suggests that light converts Limulus rhodopsin to a stable photoequilibrium mixture of rhodopsin to a stable photoequilibrium mixture of rhodopsin and metarhodopsin and that, as in squid, the lambdamax of metarhodopsin depends on pH. This conversion at pH 7.8 is associated with a small (0.7 log unit) decrease in the maximum sensitivity of the late receptor potential. Thus the component of adaptation linked to changes in rhodopsin concentration is unimportant in comparison to the "neural" component.     

Light-modulated ADP-ribosylation, protein phosphorylation and protein binding in isolated fly photoreceptor membranes

Rhodopsin (P, lambda max 480 nm) of blowfly photoreceptors R1-6 is converted by light into a thermally stable metarhodopsin (M, lambda max 565 nm). In isolated blowfly rhabdoms photoconversion of P to M affects bacterial toxin-catalyzed ADP-ribosylation of a 41-kDa protein, activates phosphorylation of opsin and induces the binding of a 48-kDa phosphoprotein to the rhabdomeric membrane. ADP-ribosylation of the 41-kDa protein is catalyzed by cholera toxin and is inhibited by P----M conversion. The 41-kDa protein might represent the alpha-subunit of the G-protein, proposed to be part of the phototransduction mechanism [Blumenfeld, A. et al. (1985) Proc. Natl Acad. Sci. USA 82, 7116-7120]. P----M conversion leads to phosphorylation of opsin at multiple binding sites: up to 4 mol phosphate are bound/mol M formed. Dephosphorylation of the phosphate binding sites is induced by photoconversion of M to P. High levels of calcium (2 mM) inhibit phosphorylation of M and increase dephosphorylation of P. Protein patterns obtained by sodium dodecyl sulfate gel electrophoresis of irradiated retina membranes show an increased incorporation of label from [gamma-32P]ATP also into protein bands of 48 kDa, 68 kDa and 200 kDa. Binding studies reveal that in the case of the 48-kDa protein this effect is primarily due to a light-induced binding of the protein to the photoreceptor membrane. The binding of the 48-kDa phosphoprotein is reversible: after M----P conversion the protein becomes extractable by isotonic buffers. These data suggest that in rhabdomeric photoreceptors of invertebrates light-activation of rhodopsin is coupled to an enzyme cascade in a similar way as in the ciliary photoreceptors of vertebrates, although there may be differences, e.g. in the type of G-protein which mediates between the activated state of metarhodopsin and a signal-amplifying enzyme reaction.     

Visual pigment spectra of the comma butterfly,<Emphasis Type="Italic"> Polygonia c-album</Emphasis>, derived from in vivo epi-illumination microspectrophotometry

The visual pigments in the compound eye of the comma butterfly, Polygonia c-album, were investigated in a specially designed epi-illumination microspectrophotometer. Absorption changes due to photochemical conversions of the visual pigments, or due to light-independent visual pigment decay and regeneration, were studied by measuring the eye shine, i.e., the light reflected from the tapetum located in each ommatidium proximal to the visual pigment-bearing rhabdom. The obtained absorbance difference spectra demonstrated the dominant presence of a green visual pigment. The rhodopsin and its metarhodopsin have absorption peak wavelengths at 532 nm and 492 nm, respectively. The metarhodopsin is removed from the rhabdom with a time constant of 15 min and the rhodopsin is regenerated with a time constant of 59 min (room temperature). A UV rhodopsin with metarhodopsin absorbing maximally at 467 nm was revealed, and evidence for a blue rhodopsin was obtained indirectly.     

Afterpotentials in dronefly retinula cells

Summary The wavelength dependence of the afterpotentials following a bright illumination was studied in single photoreceptor cells of the droneflyEristalis. Cells with only a spectral sensitivity peak in the blue were selected. As previously demonstrated, these cells contain a rhodopsin absorbing maximally at about 450–460 nm, which upon photoconversion transforms into a metarhodopsin absorbing maximally at about 550 nm (Tsukahara and Horridge, 1977).With the visual pigment initially all in the rhodopsin form, a high rate of visual pigment conversion results in an afterhyperpolarization (AHP) when the fraction of metarhodopsin remains negligible after illumination as occurs at longer wavelengths if the intensity is high. Intensive illumination at short wavelengths is followed by a prolonged depolarizing afterpotential (PDA). The magnitude of the PDA peaks at low intensities at about 450–460 nm, corresponding to the peak of the cell's spectral sensitivity (i.e. the rhodopsin peak). With increasing intensity of illumination, however, the peak shifts progressively towards 430 nm, which corresponds to the photoequilibrium with maximum metarhodopsin that can be established by monochromatic light. From this result, it is inferred that the PDA is related to the induced fall in the rhodopsin fraction. The PDA can be abolished, or knocked down, by a long-wavelength flash which reconverts remaining metarhodopsin into rhodopsin. Therefore the decline of the PDA is restrained by the existing amount of metarhodopsin. Possible theories of afterpotentials are discussed.     

Enzymatic and oxidative metabolites of lycopene

Using the post-mitochondrial fraction of rat intestinal mucosa, we have investigated lycopene metabolism. The incubation media was composed of NAD+, KCI, and DTT with or without added lipoxygenase. The addition of lipoxygenase into the incubation significantly increased the production of lycopene metabolites. The enzymatic incubation products of 2H10 lycopene were separated using high-performance liquid chromatography and analyzed by UV/Vis spectrophotometer and atmospheric pressure chemical ionization-mass spectroscopy. We have identified two types of products: cleavage products and oxidation products. The cleavage products are likely: (1) 3-keto-apo-13-lycopenone (C18H24O2 or 6,10,14-trimethyl-12-one-3,5,7,9,13-pentadecapentaen-2-one) with lambdamax = 365 nm and m/z =272 and (2) 3,4-dehydro-5,6-dihydro-15-apo-lycopenal (C20H28O or 3,7,11,15-tetramethyl-2,4,6,8,12,14-hexadecahexaen-l-al) with lambdamax= 380 nm and m/z = 284. The oxidative metabolites are likely: (3) 2-ene-5,8-lycopenal-furanoxide (C37H50O) with lambdamax = 415 nm, 435 nm, and 470 nm, and m/z = 510; (4) lycopene-5, 6, 5', 6'-diepoxide (C40H56O2) with lambdamax = 415 nm, 440 nm, and 470 nm, and m/z =568; (5) lycopene-5,8-furanoxide isomer (I) (C40H56O2) with lambdamax = 410 nm, 440 nm, and 470 nm, and m/z = 552; (6) lycopene-5,8-epoxide isomer (II) (C40H56O) with lambdamax = 410, 440, 470 nm, and m/z = 552; and (7) 3-keto-lycopene-5',8'-furanoxide (C40H54O2) with lambdamax = 400 nm, 420 nm, and 450 nm, and m/z = 566. These results demonstrate that both central and excentric cleavage of lycopene occurs in the rat intestinal mucosa in the presence of soy lipoxygenase.     

Circular dichroism of cephalopod rhodopsin and its intermediates in the bleaching and photoregeneration process.

In the bleaching process of cephalopod rhodopsin, a new intermediate was found in the conversion process from lumirhodopsin to metarhodopsin. This intermediate of octopus has an absorption peak at about 475 nm and has been named as M475. The circular dichroism value of M475 is too small to be evaluated. On the other hand, lumirhodopsin shows a negative CD at 470 nm, a positive CD at 350 nm and a large positive CD band with three peaks at 280, 287 and 295 nm. Such a large CD band in the ultraviolet region is not observed in rhodopsin, M475 and metarhodopsin. This CD seems to be mainly due to tryptophan and tyrosine residues restricted in free rotation in the protein moiety of lumirhodopsin. The intermediate in the photoregeneration process of cephalopod rhodopsin, P380, has a positive CD band at the main peak, 380 nm, and also a large positive CD band in the ultraviolet region like lumirhodopsin.     

Two forms of intermediates of frog rhodopsin in rod outer segments

Using frog rod outer segments, we measured changes of the absorption spectrum during the conversion of rhodopsin to a photosteady-state mixture composed of rhodopsin, isorhodopsin and bathorhodopsin by irradiation with blue light (440 nm) at ? 190°C and during the reversion of bathorhodopsin to a mixture of rhodopsin and isorhodopsin by irradiation with red light (718 nm) at ? 190°C. The reaction kinetics was expressed by one exponential in the former case and by two exponentials in the latter. These results suggest that rhodopsin is composed of a single molecular species, while bathorhodopsin is composed of two kinds of molecular species designated as batho₁-rhodopsin and batho₂-rhodopsin. On warming the two forms of bathorhodopsin, each bathorhodopsin converted to its own lumirhodopsin, metarhodopsin I and finally a free all-trans-retinal plus opsin. The absorption spectra of the two forms of bathorhodopsin, lumirhodopsin and metarhodopsin I were measured at ? 190°C. We infer that a rhodopsin molecule in the excited state relaxes to either batho₁-rhodopsin or batho₂-rhodopsin, and then converts to its own intermediates through one of the two parallel pathways.     

Enzymatic and oxidative metabolites of lycopene

Using the post-mitochondrial fraction of rat intestinal mucosa, we have investigated lycopene metabolism. The incubation media was composed of NAD(+), KCl, and DTT with or without added lipoxygenase. The addition of lipoxygenase into the incubation significantly increased the production of lycopene metabolites. The enzymatic incubation products of (2)H(10) lycopene were separated using high-performance liquid chromatography and analyzed by UV/Vis spectrophotometer and atmospheric pressure chemical ionization-mass spectroscopy. We have identified two types of products: cleavage products and oxidation products. The cleavage products are likely: (1) 3-keto-apo-13-lycopenone (C(18)H(24)O(2) or 6,10,14-trimethyl-12-one-3,5,7,9,13-pentadecapentaen-2-one) with lambdamax = 365 nm and m/z = 272 and (2) 3,4-dehydro-5,6-dihydro-15,15'-apo-lycopenal (C(20)H(28)O or 3,7,11,15-tetramethyl-2,4,6,8,12,14-hexadecahexaen-1-al) with lambdamax = 380 nm and m/z = 284. The oxidative metabolites are likely: (3) 2-apo-5,8-lycopenal-furanoxide (C(37)H(50)O) with lambdamax = 415 nm, 435 nm, and 470 nm, and m/z = 510; (4) lycopene-5, 6, 5', 6'-diepoxide (C(40)H(56)O(2)) with lambdamax = 415 nm, 440 nm, and 470 nm, and m/z = 568; (5) lycopene-5,8-furanoxide isomer (I) (C(40)H(56)O) with lambdamax = 410 nm, 440nm, and 470 nm, and m/z = 552; (6) lycopene-5,8-epoxide isomer (II) (C(40)H(56)O) with lambdamax = 410, 440, 470 nm, and m/z = 552; and (7) 3-keto-lycopene-5',8'-furanoxide (C(40)H(54)O(2)) with lambdamax = 400 nm, 420 nm, and 450 nm, and m/z = 566. These results demonstrate that both central and excentric cleavage of lycopene occurs in the rat intestinal mucosa in the presence of soy lipoxygenase.     

Fast Electrical Potential from a Long-Lived,Long-Wavelength Photoproduct of Fly Visual Pigment

A rapid electrical potential, which we have named the M-potential, can be obtained from the Drosophila eye using a high energy flash stimulus. The potential can be elicited from the normal fly, but it is especially prominent in the mutant norp A^P12 (a phototransduction mutant), particularly if the eye color pigments are genetically removed from the eye. Several lines of evidence suggest that the M-potential arises from photoexcitation of long-lived metarhodopsin. Photoexcitation of rhodopsin does not produce a comparable potential. The spectral sensitivity of the M-potential peaks at about 575 nm. The M-potential pigment (metarhodopsin) can be shown to photoconvert back and forth with a "silent pigment(s)" absorbing maximally at about 485 nm. The silent pigment presumably is rhodopsin. These results support the recent spectrophotometric findings that dipteran metarhodopsin absorbs at much longer wavelengths than rhodopsin. The M-potential probably is related to the photoproduct component of the early receptor potential (ERP). Two major differences between the M-potential and the classical ERP are: (a) Drosophila rhodopsin does not produce a rapid photoresponse, and (b) an anesthetized or freshly sacrificed animal does not yield the M-potential. As in the case of the ERP, the M-potential appears to be a response associated with a particular state of the fly visual pigment. Therefore, it should be useful in in vivo investigations of the fly visual pigment, about which little is known.     

Optical activity of octopus metarhodopsins.

The optical activity of octopus rhodopsin, acid metarhodopsin and alkaline metarhodopsin was studied by a sensitive and rapid CD apparatus. For sometime it has been thought that cephalopod metarhodopsins do not have any optical activity associated with their main absorption band. However, the present work shows that acid metarhodopsin in digitonin has a positive CD band at 498 nm and a negative CD band at 436 nm and alkaline metarhodopsin has a negative CD band at 381 nm. Detergent affected the wavelength of the CD peak of the visual pigments though the pattern of the spectrum was similar. From these results it is concluded that the conformation of all-trans retinal in octopus metarhodopsin is influenced by the asymmetric conformation of the protein near the retinal and therefore inducing optical activity.     

The molecular basis of adaptive evolution of squirrelfish rhodopsins

The wavelengths of maximal absorption (lambdamax) of the rhodopsins of nine squirrelfishes (N. sammara, N. argenteus, S. punctatissimum, S. microstoma, S. diadema, S. xantherythrum, S. spiniferum, N. aurolineatus, and S. tiere) and two soldierfishes (M. violacea and M. berndti) vary between 481 and 502 nm. Phylogenetic and mutagenesis analyses suggest that the common ancestor of these pigments had a lambdamax value of approximately 493 nm, and the contemporary lambdamax values were generated mostly by amino acid replacements E122M, F261Y, and A292S. The probability of observing all these amino acid replacements at specific branches of the phylogenetic tree is only 2.5 x 10(-9); it is highly unlikely that these changes have occurred by neutral evolution. Because of a close association between the lambdamax values of these pigments and the wavelengths of light available to the corresponding species, the excess number of amino acid changes at specific branches in the phylogenetic tree strongly suggests that the rhodopsins have undergone adaptive changes at various stages of the holocentrid evolution.