Table 1

Calculated depth parameters from doxyl quenching experiments

Membrane insertion depth was calculated by measuring the relative quenching efficiencies of doxyl spin labels located at different positions on the lipid acyl chains according to the methods described by Chattopadhyay and London (37). Values of z indicate distance from the center of the bilayer, in Å, and subscripts denote the doxyl pair used to calculate this distance. Each value represents the calculated average distance of the NBD label from the center of the bilayer. Errors represent half-widths of the calculated depth distributions based on molecular dynamics simulations of doxyl quenchers by Kyrychenko and Ladokhin (42). Penetration depths were determined in the presence of 250 μM [Ca²⁺] free, except in conditions labeled “EGTA.” In these cases, dashes indicate distances not determined, as no penetration was observed in EGTA without PIP₂ present. See “Experimental procedures” for details on calculations and error propagation.