Interaction of Nucleoside Diphosphate Kinase with Membranes of Bleached Bovine Retinal Rod Outer Segments. Effects of pH, Salts, and Guanine Nucleotides

N. Ya. Orlov^1* and N. Kimura²

¹Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia; fax: (0967) 79-0553; E-mail: orlov@fluor.iteb.serpukhov.su

²Department of Molecular Biology, Tokyo Metropolitan Institute of Gerontology, 35-2, Sakaecho, Itabashi-ku, Tokyo-173, Japan; fax: (81) 3-3579-4776; E-mail: nkimura@center.tmig.or.jp

^* To whom correspondence should be addressed.

Received May 28, 1997; Revision received October 23, 1997

---

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 (G_t); and 3) G_t-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 G_t. The possible participation of NDP kinase in extremely rapid photoactivation of G_t in in vivo ROS is discussed.

---

KEY WORDS: nucleoside diphosphate kinase, retinal rod outer segments, G-protein transducin, guanine nucleotides, phototransduction

---