| Abstract: | The binding of 14C]NAD to rat brain synaptic membranes is reversible and depends on incubation time, temperature and protein concentration in the reaction mixture. The value of the rate constant for 14C]NAD binding to the synaptic membranes at 24 degrees C (kl) is 1.1 X 10(-6) M-1 S-1, the rate constant for dissociation of the 14C]NAD-receptor complex (k-1) is 3.3 X 10(-3) S-1. The value of the constant for the ligand dissociation from this complex (Kd) is 3.0 nmole. Treatment of the experimental results in the Scatchard plots for the equilibrium binding of 14C]NAD to the synaptic membranes demonstrated that the receptor sites with high and low affinities for the ligand (Kd1 = 3.3 nmol, Kd2 = 14.4 nmole) and with binding capacities of 44 and 77 pmole of 14C]NAD, respectively. It was found that the synaptosomal membrane components which bind the labelled NAD have a protein nature. Data from 14C]NAD and nicotinamide-3H]NAD binding suggest that brain synaptic membranes bind NAD at the nicotinamide and adenylic moieties. |
