S-antigen has been quantitated in bovine and rat retina by electroimmunoassay. The molar ratios S-antigen to rhodops in in photoreceptor cells were close to 1:1. Immunofluorescence studies show that light induces a shift of S-antigen towards the rod outer segments where it concentrates. Assays indicate that S-antigen becomes largely water insoluble but detergent soluble under these conditions. On basis of previous ultrastructural and present results, this has been interpreted as a light induced binding of S-antigen to the rod outer segment membranes. The data support evidence from literature that S-antigen interacts with (rhod) ops in and we conclude that S-antigen plays a major role in the phototransduction process.

The 11-cis-retinol dehydrogenase (11-cis-RoDH) gene encodes the short-chain alcohol dehydrogenase responsible for 11-cis-retinol oxidation in the visual cycle. The structure of the murine 11-cis-RoDH gene was used to reinvestigate its transcription pattern. An 11-cis-RoDH gene transcript was detected in several non-ocular tissues. The question regarding the substrate specificity of the enzyme was therefore addressed. Recombinant 11-cis-RoDH was found capable of oxidizing and reducing 9-cis-, 11-cis-and 13-cis-isomers of retinol and retinaldehyde, respectively. Dodecyl-L L-1-maltoside used to solubilize the enzyme was found to affect the substrate specificity. This is the first report on a visual cycle enzyme also present in non-retinal ocular and non-ocular tissues. A possible role in addition to its role in the visual cycle is being discussed.z 1998 Federation of European Biochemical Societies.

The retinal expression pattern of RARs and RXRs is heterogeneous. The observation that RXRalpha is present in rods whereas RARalpha is present in cones, suggests a mechanism by which RA that is produced upon bleaching, could generate different responses in the two photoreceptor cell subtypes.