The Vitamin a of a Euphausiid Crustacean

Abstract

Among crustacea, the euphausiids appear to be particularly rich in vitamin A, almost all of which is concentrated in the eyes. In some species' no vitamin A at all has been detected in other tissues, or in whole bodies less the eyes. The vitamin A is peculiar in possessing a very much lower nutritional potency in rats than is exhibited by all-trans or fish liver vitamin A (Batham et al., 1950;Fisher, Kon, and Thompson, 1952, 1954.The low biopotency of euphausiid vitamin A implies that it may consist largely of low potency ds isomers (of. Kon's suggestion, 1954). The neo-a isomer (13-ds) has about 73 per cent the potency of all-trans vitamin A, the remaining natural c/s isomers only 22 to 24 per cent (neo-b, iso-a, iso-b) (Ames a al., 1955).Recently it has been shown that lobster vitamin A, almost all of which is in the eyes, consists almost entirely of the neo-b isomer (ll-ds) Burg, 1955, 1956-57).Dr. Kon has sent us for examination an oil extracted from the eyes of the euphauslid, Meganyaiphane~s ~rvegica. 24 gin. of eyes, representing several thousand animals, were extracted with petroleum ether containing 23 per cent alcohol in a Waring blendor (el. Fisher e$ al., 1952). The solvent was evaporated off, and the off sealed under nitrogen. 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. This mixture was diluted with 40 per cent its volume of water, and extracted repeatedly with petroleum ether. The absorption spectrum of the petroleum ether solution is shown in Fig. 1. It displayed a broad absorption maximum at about 317 m~, which moved to 324 m~ on isomerization with light in the presence of a trace of iodine. 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 )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

Chemistry of the Retinoid (Visual) Cycle

“…It is remarkable that a ligand, retinal, which is just slightly larger than tryptophan, when photoisomerized causes a reliable change in the conformation of rhodopsin to its activated form that couples with G protein. This activation is accomplished through geometric cis/trans isomerization of the chromophore, deprotonation of the Schiff linkage, and reorganization of water molecules within the TMD of this receptor. ,− …”