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T H Goldsmith

Publications and source records attributed to T H Goldsmith.

10 recordsLinked to original sources
PubMed1992

Retinoids in the lateral eye of Limulus: evidence for a retinal photoisomerase.

The lateral eyes of the horseshoe crab Limulus contain about 80 pmoles of retinal, 30 pmoles of retinol, and 4 pmoles of retinyl esters. More all-trans than 11-cis isomer was found in each category of retinoid. No consistent changes were observed in the amounts of retinal, retinol, or retinyl esters as a function of time of day. No 3,4-dehydro- nor hydroxyretinoids were found. Aqueous extracts of the eye support the stereospecific formation of 11-cis retinal from all-trans retinal when irradiated with light. The reaction requires a protein that is apparently recognized by polyclonal antibodies raised against the retinal photoisomerase extracted from honeybee eyes. The isomerase is able to use as substrate either endogenous all-trans retinal in the extract of retinal supplied in vesicles of phospholipid. The spectral efficiency of this isomerization has lambda max at 550 nm, but the spectrum appears too narrow compared with the absorbance spectrum of retinoid-binding proteins, probably because of inadequate correction for nonspecific isomerization at short wavelengths.

Animals↗
PubMed1991

Localization of retinal photoisomerase in the compound eye of the honeybee.

The distribution of honeybee retinal photoisomerase, a soluble light-requiring enzyme that stereospecifically forms 11-cis retinal, was investigated by immunoelectron microscopy and by HPLC. Immunolocalization with polyclonal antibodies shows that the highest concentration of retinal photoisomerase is located in the proximal portion of the primary pigment cells in large aggregates (approximately 2 microns diameter). Photoisomerase is also located in the peripheral portion of the photoreceptor cells, laterally displaced from the rhabdom, but in much lower concentration. Because of the larger volume of the photoreceptor cells, about half of the total immunoreactivity is associated with the primary pigment cells. Dissection of the eye with the subsequent use of HPLC to assay for photoisomerase activity showed that most of the photoisomerase activity is associated with tissues near the cornea. The same tissue also supports the reduction of 11-cis retinal to 11-cis retinol. These biochemical findings are consistent with the immunolocalization of retinal photoisomerase to the high-concentration aggregates in the primary pigment cells that surround the crystalline cones. The major synthesis of 11-cis retinol therefore takes place in the primary pigment cells, and the retinoid must be moved into the photoreceptor cells to be available to newly synthesized opsin. The immunoreactivity of the photoreceptor cells appears to reflect the presence of some isomerase without an attached retinoid chromophore.

Animals↗
PubMed1991

The role of retinal photoisomerase in the visual cycle of the honeybee.

The compound eye of the honeybee has previously been shown to contain a soluble retinal photoisomerase which, in vitro, is able to catalyze stereospecifically the photoconversion of all-trans retinal to 11-cis retinal. In this study we combine in vivo and in vitro techniques to demonstrate how the retinal photoisomerase is involved in the visual cycle, creating 11-cis retinal for the generation of visual pigment. Honeybees have approximately 2.5 pmol/eye of retinal associated with visual pigments, but larger amounts (4-12 pmol/eye) of both retinal and retinol bound to soluble proteins. When bees are dark adapted for 24 h or longer, greater than 80% of the endogenous retinal, mostly in the all-trans configuration, is associated with the retinal photoisomerase. On exposure to blue light the retinal is isomerized to 11-cis, which makes it available to an alcohol dehydrogenase. Most of it is then reduced to 11-cis retinol. The retinol is not esterified and remains associated with a soluble protein, serving as a reservoir of 11-cis retinoid available for renewal of visual pigment. Alternatively, 11-cis retinal can be transferred directly to opsin to regenerate rhodopsin, as shown by synthesis of rhodopsin in bleached frog rod outer segments. This retinaldehyde cycle from the honeybee is the third to be described. It appears very similar to the system in another group of arthropods, flies, and differs from the isomerization processes in vertebrates and cephalopod mollusks.

Adaptation, Ocular↗
PubMed1990

Phyletic aspects of the distribution of 3-hydroxyretinal in the class Insecta.

The distribution of 3-hydroxyretinal (R3), a recently discovered retinoid used as the visual pigment chromophore in some insects, was investigated in the class Insecta using HPLC technology. We studied 138 species in 24 orders, sampling from a wide range of taxonomic groups as well as varied habitats. In addition to groups already known to have R3, we find this retinoid in Hemiptera (suborder Heteroptera), Plecoptera, Megaloptera, and Hymenoptera. We also find retinal (R1) in Hemiptera (suborder Homoptera), Mecoptera, and Trichoptera, groups previously thought to have only R3. The pattern of R3 occurrence indicates that this retinoid cannot be considered a phylogenetic marker, having a scattered distribution in the class Insecta as well as within some orders of insects. Several environmental factors that might influence the selection of chromophore have been considered, but none correlates with its distribution. The evolutionary reasons for the pattern of occurrence of R3 therefore remain unknown.

Animals↗
PubMed1990

Optimization, constraint, and history in the evolution of eyes.

Several features of the evolution of eyes and photoreceptors are examined in an effort to explore the relative roles of adaptation and historical and developmental constraints. Optical design shows clear evidence of adaptation, which in some respects approaches optima predictable from physics. The primate fovea, on the other hand, illustrates how adaptation can be channeled by developmental heritage. The primary structures of opsins reveal multiple evolutionary lineages within both Drosophila and humans. The pigments of vertebrae rods comprise a subset of opsins whose evolutionary relationships map onto the phylogeny of the parent species. The evolutionary reasons for why most rod pigments absorb maximally at 500 +/- 10 nm are obscure, as there is no convincing explanation based on adaptation alone. Rods are appropriately distinguished from cones on the basis of which opsin gene is expressed. This criterion is likely to be in conflict with other definitions in phyletic lines (e.g., geckos, snakes) that have long diurnal or nocturnal histories accompanied by loss of one or more opsin genes, followed by a secondary adaptation to life in a different photic environment. Color vision--a generalizable perception associated with the spectral composition of light--is usefully distinguished from wavelength-specific behaviors. The latter are also based on multiple visual pigments and more than one spectral class of receptors but cannot be altered by learning. The distinction is particularly forceful in bees, which exhibit both kinds of behavior. The evolution of primate color vision has been shaped by historical factors involving an extensive period of early mammalian nocturnality. Birds, by contrast, have more elaborate cones and a richer set of visual pigments. Avian color space can be represented in a tetrahedron.

Amino Acid Sequence↗
PubMed1977

Restrictions on rotational and translational diffusion of pigment in the membranes of a rhabdomeric photoreceptor.

Individual, isolated rhabdoms from dark-adapted crayfish (Orconectes, Procambarus) were studied with a laterally incident microbeam that could be placed in single stacks of microvilli. Concentration gradients of metarhodopsin along the lengths of microvilli were produced by local bleaches, accomplished by irradiation with small spots of orange light at pH 9 in the presence of glutaraldehyde or formaldehyde. No subsequent redistribution of pigment was observed in the dark, indicating an absence of translational diffusion. On the basis of comparison with other systems, glutaraldehyde, but not formaldehyde (0.75%), would be expected to prevent diffusion of protein in the membrane. Under the same conditions photodichroism is observed, indicating an absence of free Brownian rotation. Photodichroism is larger in glutaraldehyde than in formaldehyde, suggesting that the bifunctional reagent quiets some molecular motion that is present after treatment with formaldehyde. Quantitative comparison of photodichroism with mathematical models indicates that the pigment absorption vectors are aligned within +/- 50 degrees of the microvillar axes and are tilted into the surface of the membrane at an average value of about 20 degrees. The photoconversion of rhodopsin to metarhodopsin is accompanied by an increase in molar extinction of about 20% at the lambda maxand a reorientation of the absorption vector by several degrees. The transition moment either tilts further into the membrane or loses some of its axial orientation, or both. The change in orientation is 3.5 time larger in formaldehyde than in glutaraldehyde.

Absorption↗
PubMed1975

Photoreceptor processes: some problems and perspectives.

Visual photoreceptors from both vertebrates and invertebrates are characterized by extensive elaboration of membrane which contains visual pigment (rhodopsin). Visual pigments in all phyla examined are chemically similar: the chromophore is 11-cis retinaldehyde attached by an aldimine linkage (Schiff base) to a membrane protein, opsin. The effect of light is to isomerize the chromophore to the all-trans configuration. Beyond these fundamental similarities, several specific areas are discussed in which variations and differences appear. (1) Light causes vertebrate visual pigments to bleach, liberating the chromophore. Most invertebrate visual pigments do not bleach in the light, but instead form a thermally stable metarhodopsin, with the chromophore in the all-trans configuration still attached to the opsin. (2) In the disk membranes of vertebrate rod and cone outer segments, the rhodopsin molecules are oriented with their chromophores nearly coplanar with the disks. Within this plane, however, both rotational and translational diffusion are possible. In the microvillar membranes of arthropod and cephalopod rhabdoms, on the other hand, the situation is less clear. There is evidence for some preferential orientation of chromophores that implies restrictions on Brownian rotation. (3) In the outer segments of vertebrate receptors, absorption of light by rhodopsin causes the plasma membrane to hyperpolarize due to a decrease in sodium conductance, possibly mediated by calcium ions. In most invertebrate photoreceptors, light causes a depolarization due to an increase in conductance, principally to sodium ions. A subsequent entry of calcium causes a partial repolarization of the membrane, due to a decrease in sodium conductance. (4) For vertebrate receptors, log threshold is directly proportional to the fraction of rhodopsin bleached (Dowling-Rushton relationship). The proportionality constant varies in different preparations from less than four to more than 30, and the physical basis for the relationship is unknown. For invertebrates, by contrast, the dependence of sensitivity on rhodopsin concentration is much less dramatic and may well depend simply on the probability of quantum catch. (5) In most species, vertebrate and invertebrate, the accumulation of photoproduct probably has no effect on membrane conductance, but several possible exceptions exist. (6) Photoregeneration of rhodopsin from metarhodopsin is likely an important mechanism of recovery in certain arthropods such as diurnal insects, but dark mechanisms of recovery also exist in all phyla. In no single case are they adequately understood.

Adaptation, Ocular↗
PubMed1975

Microspectrophotometry of rhodopsin and metarhodopsin in the moth Galleria.

Fresh, frozen sections of the photoreceptor layer of the compound eye of the moth Galleria have been examined by microspectrophotometry, using 4 times 8 mum measuring beams that sampled from approximately two to four rhabdoms. The principal visual pigment absorbs maximally at 510 nm (P510), and on irradiation is converted to a thermally stable, pH-insensitive metarhodopsin with lambda max at 484 nm (M484) and a 43% increase in molar extinction coefficient. Subsequently, short wavelength irradiation of the metarhodopsin photoregenerates some P510, but the absence of an isosbestic point the cycle of spectral changes is consistent with the presence of smaller amounts of violet-or ultraviolet-sensitive visual pigment(s) that also are converted to a blue-absorbing metarhodopsin. Difference spectra for both P510 and M484 were measured, using hydroxylamine. The 484-nm metarhodopsin is reversibly converted to a form with lambda max at 363 nm by high concentrations of glycerol. Dark regeneration of rhodopsin in vivo after several minutes exposure of thoroughly dark-adapted animals to full sunlight requires several days.

Animals↗