Analytical ultracentrifugation of SIRPγ, FabOX117 and SIRPγ: FabOX117 complexes. (A) Sedimentation velocity distributions for SIRPγ, FabOX117, a 2:1 and a 1:2 mixture of SIRPγ: FabOX117. Initial sedimentation distributions were analysed in SEDFIT, whereas data were subsequently fitted in SEDANAL . (B) Sedimentation equilibrium data of SIRPγ: FabOX117 were obtained at 2:1, 1:1 and 1:2 stoichiometric ratios; for clarity, only the data at 2:1 ratio is shown. Sedimentation equilibrium was attained at 15 000 rpm (black), 20 000 rpm (red), 28 000 rpm (green) and 36 000 rpm (yellow with black dots). Data were extracted with SEDFIT  and analysed in SEDPHAT . A single species model did not fit the data. The data were then fitted to an A + B ↔ C model where A is SIRPγ, B is FabOX117 and C is the 1:1 complex; this fit is represented by the solid black line going through each of the data traces.