The Vitamin a of the Lobster

Abstract

In many crustacea, including the lobster, the bulk of the vitamin A of the whole animal is concentrated in the eyes. Recently Fisher, Kon, and Thompson found that vitamin A extracted from the eyes of euphausiid crustacea has only about one half the biological potency of the same amount of the all-trans acetate or fish liver vitamin A. In the present experiments the vitamin A of the lobster eye is found to consist almost entirely of the hindered cis isomer, neo-b, the precursor in the vertebrate retina of the visual pigments rhodopsin and iodopsin. This isomer is known to have a low biological potency in the rat, only about one quarter that of all-trans vitamin A. In the lobster eye it is virtually all extractable with petroleum ether, about 30 per cent in the form of free alcohol, about 70 per cent in the form of esters. It was identified by its absorption spectrum, as derived from measurements on crude extracts, and measured directly in purified preparations; the changes in absorption which accompany isomerization; oxidation to the corresponding retinene; and synthesis from the latter of rhodopsin. The examination of an extract of euphausiid eyes, provided by Dr. Kon, also revealed the presence of neo-b vitamin A virtually alone. This may be the characteristic condition in the eyes of Eucarid crustacea. It is peculiar in that the neo-b isomer, being a sterically hindered form, is ordinarily expected to be represented in any equilibrium mixture of geometric isomers in very small amount. Apparently certain crustacea have ways of circumventing the difficulties implicit in producing and retaining this isomer, and store it in the eye virtually alone.

Dark regeneration of rhodopsin in crayfish photoreceptors.

“…But species doubtless differ in their reserves ofchromophore . For example, lobster eyes are known to contain such extensive stores of 11-cis retinol (Wald and Burg, 1957) that chromophore is unlikely to become limiting under conditions equivalent to those employed in the present work. In the crayfish, however, no matter how much recovery is slowed by longwavelength adaptation, it eventually proceeds to completion.…”

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

“…This is in contrast to some arthropods which have plentiful retinyl esters, such as lobsters (Wald & Burg, 1957), crayfish , and dragonflies (Seki et al, 1988). This is in contrast to some arthropods which have plentiful retinyl esters, such as lobsters (Wald & Burg, 1957), crayfish , and dragonflies (Seki et al, 1988).…”

The Vitamin a of a Euphausiid Crustacean

“…Simultaneously Em,x rose by a factor of 1.39, and the absorption band changed characteristically in shape. These observations with a relatively crude preparation already indicate that the bulk of this material is neo-b vitamin A (Brown and Wald, 1956)3 * This investigation was supported in part by funds from The Rockefeller Foundation and the Office of Naval Research.1 These isomerizations are slow compared with those reported previously (Brown and Wald, 1955;Wald and Burg, 1956-57). The reason is that while the earlier isom-627…”

“…It was in this form that we received it. It was examined by the same procedures as used with the lobster material (Wald and Burg, 1956-57).A sample of the oil was saponified at room temperature (about 26°C.) for 2~ hours in 6 per cent KOH in methanol.…”

“…It was in this form that we received it. It was examined by the same procedures as used with the lobster material (Wald and Burg, 1956-57).…”