[Protein kinase activity of bovine retina rod outer segments]

Dark-adapted pure bovine rod outer segments (ROS) (A280/A500--2.1) can be phosphorylated in the presence of [gamma-32P]ATP and [gamma-32P]GTP. The constant levels of phosphorylation, reached within 10--15 min, are 100 +/- 30 pmol 32P/nmol of rhodopsin for [gamma-32P]ATP and 2--4 pmol 32P/nmol of rhodopsin for [gamma-32P]GTP. These processes are not controlled by 10(-4)--10(-8) cAMP, cGMP or Ca2+, but are inhibited at higher concentrations of these agents. In the presence of histone the constant level of phosphorylation is increased up to 200 +/- 30 pmol 32P/nmol of rhodopsin for [gamma-32P]ATP, but is not changed when [gamma-32P]GTP is used. 10(-5) M cAMP is found to activate the phosphorylation in the presence of histone and [gamma-32P]ATP by 5--6 times. All this evidences that ROS contains cAMP-dependent protein kinase, which utilizes ATP, but not GTP. Moreover, ROS contains cyclic nucleotides- and Ca2+-independent protein kinase. These protein kinases are the ROS endogenous enzymes. This is shown in experiments on separation of pure ROS in a sucrose density gradient.