340
GEORGE WALD
retinene, but this is not explicitly suggested by Kampa, and is intrinsically unlikely. It seems to me in view of what is said just below
that the vitamin A found by Kampa in her extracts was also present before bleaching, and that her methods may not have been sufficiently
sensitive to detect the retinene associated with the visual pigment.
It is a remarkable property of the invertebrates so far investigated
that almost all their vitamin A is concentrated in their eyes. In the
squid Wald was unable to detect a trace of vitamin A in whole bodies
less the eyes (66). More than 90% of the total vitamin A in euphausiid
Crustacea is found in their eyes. Frequently no vitamin A at all can be
found in other tissues, or in whole bodies less the eyes. The same is true
of a number of decapod Crustacea: lobster, green crabs, and shrimp
(70).
It has recently been shown in the lobster (71) and the euphausiid
Meganyctiphanes (72) that virtually all of the vitamin A stored in the
eye is in the form of the hindered eis neo-b isomer. How these animals
can form and maintain exclusively this relatively unstable configuration
of vitamin A is an interesting problem, to which as yet we have no answer. The concentrations of vitamin A in these eyes are enormous. It
seems probable to me that some of this substance that had been extracted from the eye along with the photosensitive pigment was the
source of the vitamin A identified by Kampa (28) in her euphausiid
extracts after bleaching.
Recently a photosensitive pigment has been extracted from the eye
of the American lobster (73). It is interesting that in this instance, encouraged by the observation that rhabdomeres have a microstructure
comparable with that of vertebrate outer segments, we isolated a suspension of rhabdomere fragments by the same procedures of differential
centrifugation used to isolate the outer segments of rods and cones. A
rhodopsin was extracted with A max 515 π\μ, which on irradiation yielded
an intermediate pigment (metarhodopsin) with A max 490 m/x, possessing
a higher extinction than rhodopsin itself, and this decomposed slowly
in the dark at pH 9.3 and 29° to retinene! and opsin. The process even
at this high pH and temperature took hours to complete (half-time, 43
minutes); and probably involved the denaturation of opsin, as in the
squid. That is, here again the system physiologically may consist mainly
of the reaction:
light
Lobster rhodopsin ,
Metarhodopsin
Goldsmith (74) has succeeded in finding retinenex for the first time
in an insect eye, that of the bee. By pursuing the protein that yielded
retinene x on denaturation, he has extracted the first photosensitive pig-
GEORGE WALD
retinene, but this is not explicitly suggested by Kampa, and is intrinsically unlikely. It seems to me in view of what is said just below
that the vitamin A found by Kampa in her extracts was also present before bleaching, and that her methods may not have been sufficiently
sensitive to detect the retinene associated with the visual pigment.
It is a remarkable property of the invertebrates so far investigated
that almost all their vitamin A is concentrated in their eyes. In the
squid Wald was unable to detect a trace of vitamin A in whole bodies
less the eyes (66). More than 90% of the total vitamin A in euphausiid
Crustacea is found in their eyes. Frequently no vitamin A at all can be
found in other tissues, or in whole bodies less the eyes. The same is true
of a number of decapod Crustacea: lobster, green crabs, and shrimp
(70).
It has recently been shown in the lobster (71) and the euphausiid
Meganyctiphanes (72) that virtually all of the vitamin A stored in the
eye is in the form of the hindered eis neo-b isomer. How these animals
can form and maintain exclusively this relatively unstable configuration
of vitamin A is an interesting problem, to which as yet we have no answer. The concentrations of vitamin A in these eyes are enormous. It
seems probable to me that some of this substance that had been extracted from the eye along with the photosensitive pigment was the
source of the vitamin A identified by Kampa (28) in her euphausiid
extracts after bleaching.
Recently a photosensitive pigment has been extracted from the eye
of the American lobster (73). It is interesting that in this instance, encouraged by the observation that rhabdomeres have a microstructure
comparable with that of vertebrate outer segments, we isolated a suspension of rhabdomere fragments by the same procedures of differential
centrifugation used to isolate the outer segments of rods and cones. A
rhodopsin was extracted with A max 515 π\μ, which on irradiation yielded
an intermediate pigment (metarhodopsin) with A max 490 m/x, possessing
a higher extinction than rhodopsin itself, and this decomposed slowly
in the dark at pH 9.3 and 29° to retinene! and opsin. The process even
at this high pH and temperature took hours to complete (half-time, 43
minutes); and probably involved the denaturation of opsin, as in the
squid. That is, here again the system physiologically may consist mainly
of the reaction:
light
Lobster rhodopsin ,
Metarhodopsin
Goldsmith (74) has succeeded in finding retinenex for the first time
in an insect eye, that of the bee. By pursuing the protein that yielded
retinene x on denaturation, he has extracted the first photosensitive pig-