Interaction of nucleoside diphosphate kinase with membranes of bleached bovine retinal rod outer segments. Effects of pH, salts, and guanine nucleotides.

Soluble nucleoside diphosphate (NDP) kinase in purified bovine retinal rod outer segment (ROS) preparations exhibit equilibrium binding to bleached photoreceptor membranes. The binding is under the control of pH and concentration of salts (NaCl, KCl, CaCl2, or MgCl2). Acidic pH and low ionic strength favor the membrane-bound form. It was found that: 1) the membrane-bound NDP kinase is released by the presence of low concentrations of guanosine 5;-O-(3-thio)triphosphate (GTP[S]), GTP, and other related compounds, whereas adenosine 5;-(beta,gamma-imino)triphosphate (AdoPP(NH)P) is ineffective under similar conditions; 2) the binding of NDP kinase to bleached ROS membranes required the presence ROS G-protein transducin (Gt); and 3) Gt-depleted ROS membranes were still able to bind NDP kinase, whereas its apparent affinity was weak and unaffected by GTP[S]. These results imply that GTP[S]-dependent interaction of NDP kinase with the membranes in the presence of bleached visual pigment rhodopsin is mediated by Gt. The possible participation of NDP kinase in extremely rapid photoactivation of Gt in in vivo ROS is discussed.