Guanosine 3',5'-cyclic nucleotide binding proteins of bovine retina identified by photoaffinity labeling.

Cyclic GMP-binding proteins present in membrane fractions of bovine retina and, in particular, rod outer segments (ROS) were identified by photoaffinity labeling with 8-azido-[32P]cGMP. Two soluble proteins and two membrane-associated proteins were specifically labeled. The soluble proteins, 93 and 72 kDa, corresponded respectively to the alpha subunit of ROS cGMP phosphodiesterase and cGMP-dependent protein kinase. One of the two membrane-associated proteins, 53 kDa, was present in all particulate retinal fractions. Its function is unknown. It is distinct from cAMP-dependent protein kinase or the 63-kDa cGMP-activated channel from ROS. The second membrane-associated protein, 37 kDa, was present only in fractions that did not contain ROS. The molecular mass of this protein was similar to that of a cGMP-binding protein previously attributed to rod cells.