Fig. 2.

Inhibition by sialorphin of ³H-SP breakdown by rat renal membranes ex vivo. (a and b) Concentration-dependent inhibition by sialorphin of ³H-SP endoproteolysis by renal membranes. Each point (○) represents the percentage of 320 nM intact ³H-SP recovered and calculated as: percentage of velocity without inhibitor - velocity in the presence of inhibitor/velocity without inhibitor; * represents the mean ± SD of four determinations. Sialorphin concentration expressed in nM is plotted on a log scale in a. Representative untransformed (c) and double reciprocal (d) and Dixon (e) plots of the inhibition by sialorphin of SP breakdown by rat renal membranes. Inhibition by sialophin was measured by using ³H-SP as substrate at the concentrations indicated for c and d, and at 24 nM (▵) or 105 nM (▴) for e. The concentrations of inhibitor for c and d were 0 (•), 1.5 (○), and 4.5 μM (open rhombs).