The Porphyropsin Visual System

Abstract

1. In the rods of fresh-water and some anadromous fishes, rhodopsin is replaced by the purple photolabile pigment porphyropsin. This participates in a retinal cycle identical in form with that of rhodopsin, but in which new carotenoids replace retinene and vitamin A. 2. Porphyropsin possesses a broad absorption maximum at 522 ± 2 mµ, and perhaps a minimum at about 430 mµ. The vitamin A-analogue, vitamin A2, possesses a maximum in chloroform at 355 mµ and yields with antimony trichloride a deep blue color due to a band at 696 mµ. The retinene-analogue, retinene2, absorbs maximally in chloroform at 405 mµ and possesses an antimony chloride maximum at 706 mµ. 3. Its non-diffusibility through a semi-permeable membrane, salting-out properties, and sensitivity to chemical denaturants and to heat, characterize porphyropsin as a conjugated carotenoid-protein. 4. The porphyropsin cycle may be formulated: porphyropsin See PDF for Structure. retinene2-protein (2)→ vitamin A2-protein (3)→ porphyropsin. Isolation of the retina cuts this cycle at (3); denaturation procedures or extraction of porphyropsin into aqueous solution eliminate in addition (1) and (2). 5. The primary difference between the rhodopsin and porphyropsin systems appears to be the possession by the latter of an added ethylenic group in the polyene chain.

A photosensitive pigment of the carp retina

“…8 (Wald, 1939); I, Collins & Morton's (1950) limits; 0, difference spectra maxima (present investigation). An example of the use of Fig.…”

“…These products were found to be either vitamin A1 or vitamin A2, the former associated with rhodopsin and the latter with porphyropsin. The absorption spectra of the retinal extracts were found to fall into one of three groups; they had absorption maxima either around 500 mu (rhodopsin group), or 520 m,u (porphyropsin group) or between the two (mixtures of rhodopsin and porphyropsin) (Wald, 1938(Wald, , 1939(Wald, , 1941 However, the presence of differing amounts of yellow impurities in the extracts complicated the inter-species comparison of absorption spectra and wide limits were tolerated by Wald (1938Wald ( , 1939 in assigning a visual pigment to the rhodopsin or porphyropsin groups. Furthermore, no tests ofhomogeneity were applied.…”

“…1 Dartnall, 1952a) are shown the absorption spectra, before and after total bleaching, of an extract of pike retinae. The difference between the unbleached and bleached curves, gives the (Wald, 1939). The pike retinal extract was shown by Dartnall to contain only one photosensitive pigment.…”

“…The most recent previous investigation was that of Wald (1939) who prepared a neutral solution by treating carp retinae, which had been hardened in alum, with 1 % digitonin solution. His extract had Amax.…”

“…According to Wald (1939), porphyropsin, the visual pigment of fresh water fish, has an absorption maximum at 522 + 2 m,u. This estimate is based on the absorption spectra of extracts from five species-the white perch, the calico bass, the blue gill, the carp and the pickerel.…”