Fig. 4.

The effect of SNP on apo- and holo-TPH. TPH–CC was prepared and adsorbed to GSH-affinity beads as described and exposed to 20 μmo-phenanthroline at 4°C for 30 min to convert TPH to its apo-form (−iron). Controls (holoenzyme) were incubated with buffer alone. Beads were washed three times with 50 mm Tris-HCl, pH 7.5, at 4°C to removeo-phenanthroline. After this initial treatment, holo-TPH and apo-TPH were exposed to 100 μm SNP at 4°C for 30 min, and beads were washed free of SNP. Residual TPH activity was then determined ± ferrous ammonium sulfate (100 μm). The results are expressed as % control TPH activity (49.5 nmol of 5-HTP · min⁻¹ · mg⁻¹) and are the mean ± SEM of four independent experiments performed in duplicate. The effects of SNP and o-phenanthroline were statistically different from control in all cases by Student’st test; *p < 0.01. The effect of iron was significant only in the case of apo-TPH by Student’st test; **p < 0.01.