Cephalopod vision involves dicarboxylic amino acids: D-aspartate, L-aspartate and L-glutamate.
In the present study, we report the finding of high concentrations of D-Asp (D-aspartate) in the retina of the cephalopods Sepia officinalis, Loligo vulgaris and Octopus vulgaris. D-Asp increases in concentration in the retina and optic lobes as the animal develops. In neonatal S. officinalis, the concentration of D-Asp in the retina is 1.8+/-0.2 micromol/g of tissue, and in the optic lobes it is 5.5+/-0.4 micromol/g of tissue. In adult animals, D-Asp is found at a concentration of 3.5+/-0.4 micromol/g in retina and 16.2+/-1.5 micromol/g in optic lobes (1.9-fold increased in the retina, and 2.9-fold increased in the optic lobes). In the retina and optic lobes of S. officinalis, the concentration of D-Asp, L-Asp (L-aspartate) and L-Glu (L-glutamate) is significantly influenced by the light/dark environment. In adult animals left in the dark, these three amino acids fall significantly in concentration in both retina (approx. 25% less) and optic lobes (approx. 20% less) compared with the control animals (animals left in a diurnal/nocturnal physiological cycle). The reduction in concentration is in all cases statistically significant (P=0.01-0.05). Experiments conducted in S. officinalis by using D-[2,3-3H]Asp have shown that D-Asp is synthesized in the optic lobes and is then transported actively into the retina. D-aspartate racemase, an enzyme which converts L-Asp into D-Asp, is also present in these tissues, and it is significantly decreased in concentration in animals left for 5 days in the dark compared with control animals. Our hypothesis is that the dicarboxylic amino acids, D-Asp, L-Asp and L-Glu, play important roles in vision.
D'Aniello
Salvatore
S
Laboratory of Biochemistry and Molecular Biology, Zoological Station of Naples, Villa Comunale, 80121 Naples, Italy.
Spinelli
Patrizia
P
Ferrandino
Gabriele
G
Peterson
Kevin
K
Tsesarskia
Mara
M
Fisher
George
G
D'Aniello
Antimo
A
D000591:Amino Acid Isomerases / Q000378:metabolism; D000600:Amino Acids, Dicarboxylic / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000378:metabolism / Q000502:physiology; D001693:Biological Transport, Active / Q000502:physiology; D002417:Cattle; D026603:D-Aspartic Acid / Q000378:metabolism / Q000502:physiology; D003624:Darkness; D049832:Decapodiformes / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism / Q000502:physiology; D007668:Kidney / Q000737:chemistry; D008027:Light; D008974:Mollusca / Q000502:physiology*; D009490:Neurosecretory Systems / Q000502:physiology; D049831:Octopodiformes / Q000502:physiology; D009899:Optic Lobe, Nonmammalian / Q000737:chemistry / Q000378:metabolism; D012160:Retina / Q000737:chemistry / Q000378:metabolism; D014316:Tritium / Q000378:metabolism; D014785:Vision, Ocular / Q000502:physiology*
D000600:Amino Acids, Dicarboxylic; D014316:Tritium; D001224:Aspartic Acid; D018698:Glutamic Acid; D026603:D-Aspartic Acid; D000591:Amino Acid Isomerases; C019749:aspartate racemase