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R Hara

Publications and source records attributed to R Hara.

At least 73 records · Page 4Linked to original sources
PubMed1984

Squid m-retinochrome. Two forms of metaretinochrome.

When retinochrome absorbs light, it bleaches to m-retinochrome, which may act as a direct supplier of 11-cis-retinal to protein opsin to form rhodopsin. The present experiments were aimed at further elucidating the molecular state of m-retinochrome. Retinochrome and m-retinochome were mixed each with sodium borohydride, subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the resultant fluorescence bands were examined. The reduced retinochrome showed only one band due to N-retinyl protein, whereas the reduced m-retinochrome had two bands. When extracted with successive volumes of n-hexane, m-retinochrome released the 11-cis-retinal chromophore in a time-course consisting of fast and slow phases. These findings indicated that m-retinochrome exists in two forms, with loose and tight coupling of the chromophore to the protein moiety. Those forms were usually balanced in a molar ratio of about 1:2, and the proportion of the tight form of m-retinochrome was increased in the presence of excess 11-cis-retinal. Based upon these findings, the role of m-retinochrome in the visual cells is discussed.

Animals↗
PubMed1983

Histochemical localization of retinochrome and rhodopsin studied by fluorescence microscopy.

Retinochrome is readily reduced by sodium borohydride into an N-retinyl protein that emits visible fluorescence upon irradiation with near-ultraviolet light. Rhodopsin is also converted to a similar fluorescent product, but only when denatured with formaldehyde before reduction. Based upon this difference, retinochrome was discriminated from rhodopsin on frozen sections. The distribution of these two photopigments in various photosensitive tissues was examined by means of epifluorescence microscopy. In the octopus retina (Octopus vulgaris), the yellow-green fluorescence of reduced retinochrome was observed in both the basal regions of the outer segments and throughout the inner segments of the visual cells, while the fluorescence of reduced rhodopsin was restricted to within the rhabdomal layer of the outer segments. In the squid parolfactory vesicles (Todarodes pacificus), rhodopsin was present in the central lumen, which contains the distal processes of the photoreceptor cells, while retinochrome was detected in the myeloid bodies scattered within the vesicular wall. In the slug retina (Limax flavus), rhodopsin was found in the microvilli, and retinochrome appeared to be concentrated in the photic vesicles of the visual cells.

Animals↗
PubMed1983

Squid retinochrome. Configurational changes of the retinal chromophore.

The configurations of the retinal chromophore in light and dark reactions of squid retinochrome were investigated by means of high-performance liquid chromatography. Orange light isomerized the chromophore of retinochrome, all-trans-retinal, mainly to the 11-cis configuration in metaretinochrome. Irradiation with shorter-wavelength lights not only accelerates the photoreversal of metaretinochrome to retinochrome but also leads to a slight production of isoretinochrome (13-cis-retinochrome), yielding a photoequilibrium mixture of three kinds of retinochrome. 13-cis- and 9-cis-retinochromes are photosensitive, and are converted into metaretinochrome upon irradiation with orange light. When steadily exposed to orange light in the presence of a trace of retinochrome-protein, all of the all-trans-, 13-cis-, and 9-cis-retinals are catalytically isomerized only to the 11-cis form, although the reaction rate is reduced in the order of the retinals listed above. In the dark, 9-cis-retinochrome, like retinochrome, remains unchanged, but both meta- and 13-cis-retinochromes slowly change to retinochrome. The chromophore of 13-cis-retinochrome changes directly to the all-trans form, whereas the 11-cis chromophore of metaretinochrome goes to all-trans mainly through the 13-cis form. The direct isomerization from 11-cis to all-trans hardly occurs at temperatures as low as 20 degrees C, and shows high values of the activation enthalpy and entropy changes. Based upon these findings, the role of retinochrome in the photoreception of the visual cells is discussed.

Animals↗
PubMed1980

Retinochrome and rhodopsin in the extraocular photoreceptor of the squid, Todarodes.

The deep-sea squid, Todarodes pacificus, possesses well-developed parolfactory vesicles as extraocular photoreceptors connected with the brain. The ventral set of vesicles forms a thread approximately 3mm long and looks orange owing to photopigments. The vesicle mainly consists of receptor cells, each of which is similar in structure to the visual cell, carrying rhabdomeres in the distal process and lamellated myeloid bodies in the proximal part. Recently we noticed that a crude extract of the vesicles is capable of isomerizing retinal from all-trans to the 11-cis form in the light, and confirmed that the vesicles in fact contained retinochrome in addition to rhodopsin. This is the first time that retinochrome has been detected in any place other than ocular tissues. The optical and chemical nature of these photopigments is the same as that we have observed in the Todarodes retina. Quantitative extractions have shown that the total yield of photopigments is approximately 0.0006 in absorbance at lambda max (light path, 10 mm) per milliliter per thread of vesicles, and that the amount of retinochrome in the vesicles is roughly equivalent to that of rhodopsin. Whereas rhodopsin is located in the rhabdomal membranes, retinochrome is probably associated with lamellated structures and their derivatives in the cytoplasm. In the parolfactory vesicles, retinochrome may also cooperate with rhodopsin in the same way as has been discussed for retinal photoreception.

Animals↗
PubMed1976

Distribution of rhodopsin and retinochrome in the squid retina.

The cephalopod retina contains two kinds of photopigments, rhodopsin and retinochrome. For many years retinochrome has been thought to be localized in the inner segments of the visual cells, whereas rhodopsin is in the outer segments. However, it is now clear that retinochrome can be extracted also from fragments of outer segments. In the dark-adapted retina of Loligo pealei retinochrome is distributed half-and-half in the inner and outer segments. Todarodes pacificus contains much more retinochrome than Loligo, and it is more abundant in the outer than in the inner segments. The outer segments of Loligo contain retinochrome and metarhodopsin in addition to rhodopsin, whether squids are kept in the dark or in the light. But there is extremely little metarhodopsin (about 3% of rhodopsin) even in light-adapted eyes. The inner segments contain only retinochrome, and much less in the light than in the dark. On the other hand, retinochrome in the outer segments increases markedly during light adaptation. These facts suggest the possibility that some retinochrome moves forward from the inner to the outer segments during light adaptation and there reacts with metarhodopsin to promote regeneration of rhodopsin.

Animals↗