The Visual Pigment Cyanide Effect

Abstract

The visual pigment of the Tokay gecko (Gekko gekko) with its in situ absorption maximum at 521 nm has its spectral position at 500 to 505 nm when chloride-deficient digitonin is used for the extraction. In this case the addition of chloride or bromide to the extract restores the maximum to 521 nm. This property, characteristic of gecko pigments in general, does not occur with any of the rhodopsins that have been tested. Simple salts of cyanide, a pseudohalogenoid with an ionic radius close to those of chloride and bromide and/or its hydrolysis product attacks both this gecko pigment and rhodopsins in the dark. This is seen as a slow thermal loss of photopigment if (sodium) cyanide is present at concentrations above 40 mM for the gecko pigment and 150 mM for the rhodopsins of the midshipman (Porichthys notatus) and of the frog (Rana pipiens). In all cases the loss of the photopigment is accompanied by the appearance of a spectral product with maximum absorption at about 340 nm. Cyanide addition has no effect on the photosensitivity of the native pigments and neither does it alter, as do chloride, bromide and other anions, the spectral absorbance curve. The spectral product at 340 nm also appears when the visual pigments are photolyzed in the presence of cyanide salts below the threshold concentrations given above. Incubation of digitonin-solubilized all-trans-retinal with (sodium) cyanide leads to a reaction product with absorption spectrum similar to that obtained with visual pigments under comparable conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro identification of rhodopsin in the green alga Chlamydomonas

“…The visible absorption of detergent-extracted S2 membranes is only 8 nm blue shifted compared to the threshold action spectra for phototaxis of wild-type or irradiated FN68 cells that were reported to peak at 503 nm (Foster et al, 1984) and accurately matches the action spectra for flash-induced responses (maxima near 495 nm; Uhl & Hegemann, 1990). Slight changes of the absorption maximum may be caused by physical and chemical alterations of the rhodopsin environment during preparation, as it has been observed for example in the case of gecko rhodopsin (Crescitelli, 1989) and halorhodopsin from Halobacteria (Grossjean & Tavan, 1987). The total amount of the retinal protein as determined in the reconstitution assay in S2 membranes allows an estimation of at least 7200 molecules/cell.…”