Visual pigments of the pigeon (Columba livia)

Abstract

Abstract Aqueous 4 % digitonin extracts have been prepared from photoreceptors isolated by the sucrose technique from the retinae of dark-adapted pigeons. These extracts have been analysed by the method of partial bleaching, and have been found to contain two photosensitive pigments. One of these pigments has extinction maximum at 502 mμ. The other, which accounts for 13 to 16 per cent of the total pigment present, has extinction maximum at 544±3 mμ. Both pigments are based on vitamin A1 and have been designated pigeon rhodopsin and visual pigment 544 respectively. Unlike the rhodopsin component, visual pigment 544 is rapidly destroyed at pH 8.8. It is quite stable at pH 6.3 to 6.6. A partial separation of the photoreceptors containing these two pigments has been achieved. Thus by gently stirring the excised retinae in 0.9 % saline it has been found that as much as 82 per cent of the total visual pigment 544 compared with only 52 per cent of the total rhodopsin is found in the tissues separated from the main bulk of the retina. By shaking dried pigeon retinae with petroleum ether and chromatographing the resulting extract, it has been possible to isolate two carotenoids. One of these is astaxanthin, whilst the other corresponds to a carotenoid previously isolated from the chicken retina, and is possibly sarcinin or sarcinaxanthin. The relationship between the pigeon's visual pigments and its visual sensitivity has been discussed.