C. Bridges
Jun 1, 1977
Citations
2
Influential Citations
41
Citations
Quality indicators
Journal
Experimental eye research
Abstract
Abstract The utilization of aqueous colloidal dispersions of 11-cis retinol, retinal and their 9-cis isomers has been investigated in fragmented and intact frog rod outer segments, the latter while still attached to the retina. The fragments efficiently utilize 75–80% of added 11-cis retinal for rhodopsin regeneration, but this proportion drops to about 2% when the plasma membrane is left intact. The corresponding figures for 11-cis retinol are 25 and 0·6% respectively, the former with a NADP+ supplement (NAD+ is less efficacious), the latter with endogenous cofactor. These results suggest that the plasma membrane is an effective barrier to these vitamin A compounds in the form administered. Since the plasma membrane is impermeable to NAD+ and NADP+, the ROS do not lose these cofactors unless fragmented, nor can they take them up if they are added to the external medium. Formation of isorhodopsin is observed if the 11-cis isomers are replaced by 9-cis. Activity of the 11-cis retinol oxidase is reduced or abolished by washing the ROS fragments (water, 0·64% NaCl or 5 m m -EDTA), storage at −20° or in the presence of 0·1% Triton X-100. These procedures do not affect all-trans retinal reduction, so it is concluded that the oxidase is a separate entity. Reduction of all-trans retinal can be linked with oxidation of 11-cis retinol through the common cofactor NADP(H), so that a coupled cofactor recycling system may exist during light-adaptation in vivo, where bleaching and regeneration occur simultaneously.