scholarly journals THE VITAMIN A OF THE LOBSTER

1957 ◽  
Vol 40 (4) ◽  
pp. 609-625 ◽  
Author(s):  
George Wald ◽  
Stanley P. Burg
Keyword(s):  
Vitamin A ◽  
Equilibrium Mixture ◽  
Visual Pigments ◽  
Geometric Isomers ◽  
Free Alcohol ◽  
Fish Liver ◽  
Biological Potency ◽  
B Vitamin ◽  
Cis Isomer ◽  
Lobster Eye

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.

scholarly journals RETINENE ISOMERASE

1956 ◽  
Vol 39 (6) ◽  
pp. 935-962 ◽  
Author(s):  
Ruth Hubbard
Keyword(s):  
Aqueous Solution ◽  
Vitamin A ◽  
Dark Adaptation ◽  
Pigment Epithelium ◽  
Equilibrium Mixture ◽  
Dehydrogenase System ◽  
Dominant Process ◽  
B Vitamin ◽  
Cis Isomer

Rhodopsin is formed by the condensation of opsin with a cis isomer of retinene, called neo-b. The bleaching of rhodopsin releases all-trans retinene which must be isomerized back to neo-b in order for rhodopsin to regenerate. Both retinene isomers are in equilibrium with the corresponding isomers of vitamin A, through the alcohol dehydrogenase system. An enzyme is found in cattle retinas and frog pigment layers which catalyzes the interconversion of all-trans and neo-b retinene. We call it "retinene isomerase." It is soluble in neutral phosphate buffer, and precipitates between 20 and 35 per cent saturation with ammonium sulfate. In the dark, the isomerase converts all-trans and neo-b retinene to an equilibrium mixture of 5 parts neo-b and 95 parts all-trans. With opsin present to trap neo-b, the isomerase catalyzes the synthesis of rhodopsin from all-trans retinene. This reaction, however, is too slow to account for dark adaptation. Retinene is isomerized by light, but too slowly to supply the retina with neo-b. In aqueous solution the pseudoequilibrium mixture contains about 15 per cent neo-b. When all-trans retinene is irradiated in the presence of isomerase, the rate of formation of neo-b is increased about 5 times, and the pseudoequilibrium shifted so that the mixture now contains about 32 per cent neo-b. The isomerase is specific for all-trans and neo-b retinene. It does not act on two other cis isomers of retinene, nor on all-trans or neo-b vitamin A. The role of the isomerase in vision appears to be as follows: in the light, as rhodopsin is bleached to opsin and all-trans retinene, the latter is in part converted to the neo-b isomer and stored in the pigment epithelium as neo-b vitamin A. During dark adaptation, the dominant process is the trapping by opsin of neo-b retinene supplied from stores of neo-b vitamin A, and the slow isomerase-catalyzed "dark" conversion of all-trans to neo-b retinene.

ISOMERIZATION OF 11-cis VITAMIN A IN VIVO

1960 ◽  
Vol 38 (11) ◽  
pp. 1219-1222 ◽  
Author(s):  
D. W. Stainer ◽  
T. K. Murray ◽  
J. A. Campbell
Keyword(s):  
Vitamin A ◽  
Intestinal Tract ◽  
Biological Potency ◽  
Oral Doses ◽  
Poor Absorption ◽  
Cis Isomer

Single oral doses of all-trans and 11-cis vitamin A acetate were given to young, vitamin A deficient rats and the proportion of cis isomer in the intestinal tract and liver measured. Some conversion of 11-cis to all-trans occurred in the stomach and intestine, and a mixture of the two isomers was absorbed and stored in the liver. The high proportion of cis isomer found in the liver stores 5 hours after a dose of 11-cis vitamin A disappeared completely in 23 days. Oral doses of both all-trans and 11-cis vitamin A produced greater liver stores than the same doses given subcutaneously. The relative biological potency of the 11-cis isomer was the same by either route, which indicated that the low potency of this isomer was not due only to poor absorption from the intestine.

ISOMERIZATION OF 11-cis VITAMIN A IN VIVO

1960 ◽  
Vol 38 (1) ◽  
pp. 1219-1222 ◽  
Author(s):  
D. W. Stainer ◽  
T. K. Murray ◽  
J. A. Campbell
Keyword(s):  
Vitamin A ◽  
Intestinal Tract ◽  
Biological Potency ◽  
Oral Doses ◽  
Poor Absorption ◽  
Cis Isomer

Single oral doses of all-trans and 11-cis vitamin A acetate were given to young, vitamin A deficient rats and the proportion of cis isomer in the intestinal tract and liver measured. Some conversion of 11-cis to all-trans occurred in the stomach and intestine, and a mixture of the two isomers was absorbed and stored in the liver. The high proportion of cis isomer found in the liver stores 5 hours after a dose of 11-cis vitamin A disappeared completely in 23 days. Oral doses of both all-trans and 11-cis vitamin A produced greater liver stores than the same doses given subcutaneously. The relative biological potency of the 11-cis isomer was the same by either route, which indicated that the low potency of this isomer was not due only to poor absorption from the intestine.

scholarly journals THE VITAMIN A OF A EUPHAUSIID CRUSTACEAN

1957 ◽  
Vol 40 (4) ◽  
pp. 627-634 ◽  
Author(s):  
George Wald ◽  
Paul K. Brown
Keyword(s):  
Absorption Spectrum ◽  
Vitamin A ◽  
Good Accord ◽  
Meganyctiphanes Norvegica ◽  
B Vitamin ◽  
Cis Isomer

The vitamin A of the euphausiid crustacean, Meganyctiphanes norvegica, consists almost wholly of the hindered cis isomer, neo-b (11-cis). In this animal vitamin A is concentrated almost entirely in the eyes; and its properties so closely resemble those of pure neo-b vitamin A as not in themselves to indicate that any other isomer is present. However, Fisher et al. (1955 b) have isolated a small fraction from this material which may be neo-c vitamin A (11, 13-dicis). The neo-b isomer was identified by its absolute absorption spectrum, the changes of absorption spectrum on isomerization, oxidation to neo-b retinene, and synthesis from the latter of rhodopsin. This identification is also in good accord with new, revised bioassays of Meganyctiphanes vitamin A by Plack et al. (1956).

scholarly journals The Biological Potency of Vitamin A in Whale Liver Oil and its Molecular Distillates

1950 ◽  
Vol 16 (2) ◽  
pp. 46-52 ◽  
Author(s):  
K. SABASI ◽  
A. NAKAYAMA ◽  
S. HIRAO ◽  
T. KINUMAKI
Keyword(s):  
Vitamin A ◽  
Biological Potency

scholarly journals Studies on Antioxidants for Vitamin A in Fish Liver Oil. II

1955 ◽  
Vol 75 (3) ◽  
pp. 274-277 ◽  
Author(s):  
Tomohiko Kawai ◽  
Tsunekazu Shimizu ◽  
Hisae Chiba
Keyword(s):  
Vitamin A ◽  
Fish Liver

State of Vitamin A in Fish Liver Oils

1945 ◽  
Vol 17 (8) ◽  
pp. 499-503 ◽  
Author(s):  
Henry M. Kascher ◽  
James G. Baxter
Keyword(s):  
Vitamin A ◽  
Fish Liver

The photoreceptors and visual pigments in the retina of the white sturgeon, Acipenser transmontanus

1990 ◽  
Vol 68 (7) ◽  
pp. 1544-1551 ◽  
Author(s):  
A. J. Sillman ◽  
M. D. Spanfelner ◽  
E. R. Loew
Keyword(s):  
Vitamin A ◽  
Visual Pigment ◽  
Visual Pigments ◽  
Spectrophotometric Analysis ◽  
White Sturgeon ◽  
Acipenser Transmontanus ◽  
Light Regimen ◽  
Cone Pigment ◽  
Spectral Absorbance

The photoreceptors in the retina of the white sturgeon, Acipenser transmontanus (Chondrostei), were studied by means of scanning electron microscopy, in situ microspectrophotometry, and spectrophotometric analysis of visual pigment extracts. The white sturgeon retina is simple in that it contains only two morphologically distinct photoreceptors. The retina is dominated by rods with large outer segments, but there is a substantial population (40%) of single cones. Evidence was found for only one rod visual pigment and one cone visual pigment. Peak spectral absorbance (λmax) of the rod pigment is near 539 nm, whereas λmax of the cone pigment is near 605 nm. Both visual pigments are porphyropsin types with chromophores based on vitamin A2. No detectable rhodopsin based on vitamin A1 is ever present, regardless of season or light regimen. The results are discussed in terms of the sturgeon's behavior, as well as the implications for the evolution of color vision.

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