8-Azido-ATP (alpha 32P) binding to rod outer segment proteins.

ATP has important roles in the vertebrate rod outer segment (ROS) physiological response to light. One of them is the quench of light-activated cGMP-phosphodiesterase activity. How ATP quenches PDE is not established; however, leading hypotheses favor the intervention of a 48-kDa ATP-binding protein and/or an ATP-utilizing rhodopsin kinase in this reaction. We have investigated the binding of [alpha 32P]8-azido-ATP to rat ROS proteins in the presence and absence of various divalent cations and competitive nucleotides. An event we have detected which might further clarify the role of ATP in PDE inactivation is a zinc-induced binding of azido-ATP to rhodopsin. Manganese is also effective in inducing this binding, while magnesium and calcium are not. The azido-ATP binding is eliminated by the addition of ATP, but not GTP, UTP, cGMP, or cAMP. A nucleotide-binding site on the rim protein is also suggested from these studies.