Use of a Fixed Charge Model to Determine the pK of the Negative Sites on the External Membrane Surface

A magnitude change has also been observed for the sodium conductance of the frog node, with an apparent pK of about 5.2 (Hille, 1968;Drouin and The, 1969).This value is in good agreement with the apparent pK of 5.3 calculated from the measurement of voltage shift.The pK value for a free carboxyl group is 4.8 (Edsall and Wyman, 1958), which is very close to the calculated pK at the membrane surface of 4.6.This is consistent with the idea that a carboxyl group on a fatty acid chain is responsible for the surface charge.