Photochemistry and biochemistry of blowfly photoreceptor membranes

Abstract

s 1701 (J'max ~ 660 nm) originating from the visual pigment in the rhabdomeres is directly proportional to the metarhodopsin concentration and not noticeably affected by hypoxia or by temperature changes. In flies with low photopigment content the red emission remains negligibly. (II) Green emission (J'max m, 520-530 nm) originating from the photoreceptor cell bodies is found equally in visual pigmentrich and -deprived flies. Illumination of a dark adapted eye induces an instant increase of blue-induced green emission. After a few seconds a plateau is reached through a biphasic time course. This dynamic effect is highly temperature dependent and vanishes under hypoxia conditions. Presumably the green emission is mainly due to mitochondrial flavoproteins. (III) Blue emission (2max ~ 460-470 nm), also coming from the cell bodies, is induced by ultraviolet light. Upon illumination this emission decreases with a time course very similar to that of the green emission increase. A likely candidate for the blue fluorescing pigment is NADH residing in the photoreceptors' mitochondria and in the cell soma. RHODOPSIN IN FISH IRIDOCYTES J. N. LYTHGOE, JULIA SHAND and R. G. FOSTER Department of Zoology, University of Bristol, Bristol BS8 lUG, England The neon tetra, which is often kept in tropical aquaria, has an iridescent lateral stripe, which is a dull violet at night and a brilliant green in the daytime. This colour change is induced by the direct action of light and results from a change in spacing of a stack of quarter-wave plates of alternating layers of guanine and cytoplasm in the dermal iridocytes. Immunofluorescence studies using cattle and quail rhodopsin, raised in rabbit, as the antigen indicate that an opsin-based visual pigment is present in the multilayer stack of the iridocyte itself. STRUCTURES AND FORMATION OF THE CAROTENOIDS OF AVIAN AND REPTILIAN RETINAS BRIAN H. DAVIES, ALAN AKERS, BETHAN W. DAVIES, ROSEMARY J. LEWIS-JONES, SUSAN POLLARD and ANN J. SHUFFLEBOTHAM Department of Biochemistry and Agricultural Biochemistry, The University College of Wales, Penglais, Aberystwyth, Dyfed SY23 3DD, Wales The structures of all the avian retinal oil droplet carotenoids are established and stereochemistry has been determined in relevant cases. Most of our work has been on turkey retinas, but the carotenoids of chicken, duck and goose retinas are qualitatively the same. The minor carotenoids are unremarkable, zeaxanthin /~-cryptoxanthin and lutein being common dietary components, but the three main carotenoids have all had their chromophores extended or shortened, thus providing potential cut-off filters with a wide range of spectra. Mechanisms have been postulated for the formation of these three, galloxanthin, astaxanthin and e,e-carotene, from yolk zeaxanthin in embryo. Administration of radioactive zeaxanthin to fertile eggs resulted in radioactivity accumulating in the retina on day 19/20 of incubation, e,e-Carotene, the sole hydrocarbon carotenoid of avian retinas is the sole carotene also in retinas of the green turtle, Chelonia mydas. A MICROSPECTROPHOTOMETRIC STUDY OF THE VISUAL PIGMENTS AND OIL DROPLETS FOUND IN THE RETINA OF THE AYLESBURY DUCK (Anas platyrynchos domesticus ) S. D. JANE and J. K. BOWMAKER School of Biological Sciences, Queen Mary College, University of London, Mile End Road, London E1 4NS, England Microspectrophotometric measurements of the visual receptor cells of Aylesbury ducks suggest that they are trichromatic with cone pigments having 2ma~ values at approximately 420, 500 and 570 nm. The rod