FIGURE 4.
X-ray Guinier analyses of ln I(Q) versus Q2 for C3, C3u, C3b, C3c, and C3d titrated with zinc. For clarity, the 10–13 domains of C3, C3u, C3b, and C3c are depicted as schematics. In all panels, the open symbols correspond to the experimental data, and the filled symbols correspond to those used for the Guinier straight line fits. The Q fit range was 0.14–0.22 nm−1 in all cases (arrow ranges), and the zinc concentrations in micromolar are numerically labeled as shown. The Guinier RG plots are shown for C3 (A), C3u (B), C3b (C and F), and C3c (D), all at ∼4 μm, and for C3d (E) at 14.5 μm. The ZnSO4 concentrations were 2 μm (○), 6 μm (▵), 20 μm (□), and 60 μm (▿), all shown in black, and 120 μm (○), 200 μm (▵), and 600 μm (□), all shown in gray. In F, the C3b Guinier plots from C are displaced in steps of 0.2 log units to show the processes of aggregation and precipitation more clearly.