(a,b,c) Ca2+-dependent and (d,e,f) Ca2+-independent partitioning of C2AB fragment into (a,d) PtdChol/PtdSer, (b,e) PtdChol/ PtdIns(4,5)P2 and (c,f) PtdChol/PtdSer/ PtdIns(4,5)P2 bilayers. (d,e) No binding of the KAKA mutant was observed in the presence of PtdSer or PtdIns(4,5)P2 alone in absence of calcium . At equivalent charge densities, removal of lysine residues within the polybasic face reduced the membrane affinity in vesicles containing PtdSer and PtdIns (4,5)P2 (c) more than it did in vesicles containing either (a) PtdSer or(b) PtdIns (4,5)P2 in the presence of calcium. The lines represent fits to the data using Eq  (Materials and methods). Reciprocal molar partition coefficients obtained from data are listed in Tables 2 and 3 (n = 2–3).