Effect of light on the transfer of sugars from sugar nucleotides to rod outer segment membranes of control and dystrophic rats.

The transfer of N-acetyl-D-glucosamine (GlcNAc), D-mannose (Man), D-galactose (Gal) and L-fucose (Fuc) from their nucleotide complexes to isolated rod outer segment (ROS) membranes obtained from dark-adapted 21 +/- 2 days old dystrophic (RCS) and control (RCS-rdy+) rat retinas, was studied under light or dark conditions of incubation. It was found that all of these sugars were transferred to ROS membranes in the dark. Under these conditions there was significantly less (p less than 0.001) Gal transferred to dystrophic than to control membranes. Exposure to light affected the transfer of Gal and Fuc only. Thus, the transfer of Gal and Fuc to control ROS membranes was increased by about 50% compared to the level observed under dark conditions of incubation. On the other hand, exposure to light had no effect on the transfer of Gal to dystrophic ROS membranes but it enhanced the transfer of Fuc to these membranes by about 250% above the level observed in the dark. Under light there were highly significant (p less than 0.001) differences between control and dystrophic membranes in the transfer of Gal and Fuc. The transfer of Fuc to dystrophic ROS membranes was proportional to the concentration of GDP-Fuc but the acceptors on control membranes were saturated at low concentrations of substrate. However, the transfer of Gal from UDP-Gal to both types of membranes was proportional to the concentrations of substrate and ROS membrane protein and to the period of incubation. The transfer of Gal and Fuc to both types of membranes was significantly reduced after denaturation of ROS membrane proteins.(ABSTRACT TRUNCATED AT 250 WORDS)