Lectin binding sites on the outer segment membranes of photoreceptor cells in the pineal organ of Lampetra planeri (Cyclostomata).

The glycoproteins of the outer segment membrane of photoreceptor cells in the pineal organ of Lampetra planeri were studied using the affined properties of lectins to sugar moieties. Among five different lectins, labelled with fluorescein-isothiocyanate, Concanavalin A (Con A) and wheat germ agglutinin (WGA) induced an intense fluorescence on the large outer segments protruding into the lumen of the pineal organ. The complementary sugars, alpha-D-mannopyranosyl (for Con A) and N-acetyl-D-glucosamine (for WGA), inhibit the binding of both lectins. By means of electron microscopy, after incubation in Con A and labelling with peroxidase, and intense enzymatic activity was revealed in the diskal spaces by the technique of Graham and Karnovsky (1966). These results suggest the presence of glycoproteins rich in mannose and N-acetyl-D-glucosamine thus implying the presence of a photopigment of similar composition and structure to that of rhodopsin or rhodopsin itself.