The deep-sea bioluminescent squid, Watasenia scintillans, has three visual pigments: The major one (A1 pigment) is based on retinal and has 2max=484 nm, the second one (A2 pigment) is based on 3-dehydroretinal and has 2m~x = 500 rim, and the third one (A4 pigment) is based on 4-hydroxyretinal and has )[m.x = 470 nm. The distribution of these 3 visual pigments in the retina was studied by HPLC analysis of the retinals in retina slices obtained by microdissection. It was found that A1 pigment was not located in the specific region of the ventral retina receiving the down-welling light which contains very long photoreceptor cells, forming two strata. A2 and A4 pigment were found exclusively in the proximal pinkish stratum and in the distal yellowish stratum. The role of these pigments in the retina is hypothesized to involve spectral discrimination. The extraction and analysis of retinoids to determine the origin of 3-dehydroretinal and 4-hydroxyretinal in the mature squid showed only a trace amount of 4-hydroxyretinol in the eggs. Similar analysis of other cephalopods collected near Japan showed the absence of A2 or A4 pigment in their eyes.
Walo~e'nia scintillans, a bioluminescent deep-sea squid, has a specially developed eye with a large open pupil and three visual pigments. Photoreceptor cells (outer segment: 476 #m; inner segment: 99 #m) were long in the small area of the ventral retina receiving downwelling light, whereas they were short (outer segment: 207/zm; inner segment: 44/~m) in the other regions of the retina. The short photoreceptor cells contained the visual pigment with retinal ('Area ~ ~ 484 nm), probably for the purpose of adapting to their environmental light. The outer segment of the long photoreceptor cells consisted of two strata, a pinkish proximal area and a yellow distal area. The visual pigment with 3-dehydroretinal ~ ~ 500 nm) was located in the pinkish proximal area, giving high sensitivity at longer wavelengths. A newly found pigment (Xm~ ~ 471 nm) was in the yellow distal area. The small area of the ventral retina containing two visual pigments is thought to have a high and broad spectral sensitivity, which is useful for distinguishing the bioluminescence of squids of the same species in their environmental downwelling light. These findings were obtained by partial bleaching of the extracted pigment from various areas of the retina and by high-performance liquid chromatographic analysis of the chromophore, complemented by microscopic observations.
a b s t r a c tThe arm light organ of the firefly squid, Watasenia scintillans, emits extremely bright flashes of light, which are caused by a luciferin-luciferase reaction involving ATP, Mg 2+ and molecular oxygen. The molecular mechanism underlying the bioluminescence reaction has remained unresolved, because the luciferase could not be identified or isolated. The arm light organ contains numerous rod-like bodies that are 2-6 lm long and 1-2 lm thick. This paper addresses the characterization of the extracted rod-like body. We found that the rod-like bodies emit the light in vitro by the luciferin-luciferase reaction. Furthermore, by using the X-ray powder diffraction method, we confirmed that the rod-like bodies are well-ordered microcrystals.
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