314
GEORGE WALD
—and their corresponding aldehydes, retinene! and retinene 2 , which
differ only in the possession by the latter of one added double bond in
the ring (I).
CH,
1
H
C
C
CH 3
1
c
H
C
CH 3
1
C
·\κ\/\κ\κ\,
x p
N n
N ri
N n
N
r<
J,/
CH
*
H
, /
X CH 3
C
H 2
H
H
H
CH 2 OH
H 2 C
CH 3
I
Vitamin Ai, Ci 9 H 27 CH 2 OH C
C=0
Retinenei, Ci 9 H 27 CHO: / \
/H
C
H
CH 3
CH 3
CH 3
|
H
|
H
|
C
C
C
C
C
CH 2 OH
/\κ\/\κ\/\κ
HC
C
C
C
C
C
HC
C
H
H
H
H
H
CH 3
CH 3
CH 3
Vitamin A 2 , Ci 9 H 25 CH 2 OH C
C=0
Retinene 2 , Ci 9 H 25 CHO: / \
/H
C
H
(I)
There are also two families of proteins, called opsins, one found in
rods (scotopsins), the other in cones (photopsins). Combinations of the
two retinenes with the two opsins yield the four known pigments of
vertebrate vision as shown.
Retinene
Opsin
Photosensitive Pigment
\ max (τημ)
Retinene! + Rod opsin —» Rhodopsin
500
Retinene 2 + Rod opsin —» Porphyropsin
522
Retinene! + Cone opsin -> Iodopsin
562
Retinene 2 + Cone opsin —> Cyanopsin
620
The A max cited here for rhodopsin or porphyropsin is a prevalent
value; A max may differ considerably from this in individual instances, of
which more later. The A max cited for iodopsin is that of the chicken and