Relationship of vesicle curvature and PS content to inhibition of the factor Xase complex by lactadherin or annexin V.

Sonicated vesicles (▴ and ▵), extruded vesicles (● and ○), and LMVs (▪ and ■) contained 4% PS (upper row) or 15% PS (lower row). Effective concentrations of the vesicles for supporting the factor Xase complex were identified in phospholipid titration experiments (A,D). Subsaturating phospholipid concentrations were selected for inhibition experiments (open symbols; A,D). Lactadherin was an effective inhibitor of Xase activity regardless of membrane curvature or PS content (B,E). In contrast, inhibition by annexin V was inversely related to curvature and directly related to PS content (C,F). Experimental conditions were as described in “Materials and methods” and in the Figure 1 legend. The Ca⁺⁺ concentration was 1.5 mM for sonicated vesicles of 4% PS (▴, A-C) and 5 mM for all other conditions. Data are from a single set of experiments representative of 2 or 3 experiments for all conditions.