Thin layer chromatography of retina extracts from Calliphora yielded, instead of retinal (or retinaloximes after NH2OH treatm ent) a considerably more polar aldehyde or its corresponding oximes. That these compounds originate from the chrom ophoric group of the visual pigment was shown by the occurrence of different stereoisomers in the extracts depending on the colour with which the intact visual pigment complex was previously illuminated. The absorbance maximum of the oxime found after blue illumination is the same as that of all-trans-retinal-oxime (356 nm). This spectral accordance means that previous spectral evidence for retinal as the chromophoric group of fly visual pigment is not conclusive. Flies raised on a carotenoid deficient diet enriched with the hydroxy-xanthophyll lutein possess a high visual pigment content. This points to a hydroxy- xanthophyll as a possible precursor of the chromophoric group
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