FIGURE 2.

Guanylate kinase activity assay. Activity determination of GUK in a spectrophotometric assay. The 5′-GMP to GDP conversion is coupled to NADH oxidation and the decrease in absorption is measured at 340 nm. Effect of varying RD3 concentrations on enzyme activity was tested. GUK in a soluble extract from bovine ROS (A) and GUK from porcine brain (B) were used. Normalization value 1.0 in (A) corresponds to GUK activities in the absence of RD3, which were between 0.025 and 0.042 U/mg rhodopsin. The experiment was repeated independently three times with two to three replicates for each sample yielding similar results. Statistical analysis was performed using GraphPad Prism V5.01 (GraphPad Prism Inc.). The data failed the Kolmogorov–Smirnov normality test. Therefore, the Kruskal-Wallis one-way ANOVA with post hoc tests (Dunn’s Multiple Comparison) were applied to determine if groups were significantly different from each other (significance levels are ns = p > 0.05, ^∗p ≤ 0.05, ^∗∗p ≤ 0.01, ^∗∗∗p ≤ 0.001).