Figure 4.

HrpZ binding to phosphatidic acid (PA) shows no cooperativity at low harpin concentrations. (A) HrpZ binding to immobilized PA, determined by enzyme‐linked immunosorbent assay (ELISA), was saturated at HrpZ concentrations higher than 100 µg/L (2.6 nm). Nonspecific binding to wells not coated with lipids (diamonds) was subtracted from the binding to wells coated with PA (open triangles) to obtain PA‐specific binding (filled triangles). n= 4; the error bars indicate the standard deviation. (B) Hill blot of the PA‐specific binding is linear in the middle range, with a slope of 1.08, suggesting that the soluble form of HrpZ binds to PA in a noncooperative manner. The saturation (Y) was assumed to be 100% at an absorbance difference of 2.0.