Interaction between the main components of the vertebrate retinal rod phototransduction system in solutions of detergent n-nonyl-β-D-glucoside

Abstract

cGMP-Specific phosphodiesterase (PDE6) is the key enzyme of the phototransduction system of vertebrate retinal rod outer segments (ROS). The properties of PDE in extracts prepared by solubilization of bovine ROS in a high concentration (0.5% w/v) of detergent n-nonyl-β-D-glucoside (NG) and following centrifugation (ROS-NG) have been studied. Basal PDE activity of the preparations was low, but it greatly (>50-fold) increased (up to ∼20 μmol cGMP hydrolyzed/min per mg rhodopsin (R)) in the presence of trypsin. In bleached GTPγS-containing preparations the specific PDE activity was dependent on ROS-NG concentration and was half-maximal at about 0.8 μM of ROS G protein transducin (Gt). In dark-adapted GTPγS-containing ROS-NG preparations bleaching of 0.2% of the rhodopsin resulted in half-maximal PDE activation. The same result was obtained when PDE in dark-adapted ROS-NG preparations was activated by addition of a highly purified bleached rhodopsin solubilized by 0.5% solution of NG. The results demonstrate that the presence of NG has no significant influence either on the properties of the main ROS phototrans-duction system elements (R, Gt and PDE) or on the interaction between photoactivated R and Gt and suggest that the detergent NG can be used for crystallization of the rhodopsin-transducin complex.