Phosphatidylethanolamines membrane potentials

How do protons move from the pumping sites to ATP synthase molecules Since protons, as H3O+, are sufficiently mobile, ordinary diffusion may suffice. Because of the membrane potential they will tend to stay close to the membrane surface, perhaps being transported on phosphatidylethanolamine head groups (see Chapter 8). According to the view of... 

Koryta et al. [48] first stressed the relevance of adsorbed phospholipid monolayers at the ITIES for clarification of biological membrane phenomena. Girault and Schiffrin [49] first attempted to characterize quantitatively the monolayers of phosphatidylcholine and phos-phatidylethanolamine at the ideally polarized water-1,2-dichloroethane interface with electrocapillary measurements. The results obtained indicate the importance of the surface pH in the ionization of the amino group of phosphatidylethanolamine. Kakiuchi et al. [50] used the video-image method to study the conditions for obtaining electrocapillary curves of the dilauroylphosphatidylcholine monolayer formed on the ideally polarized water-nitrobenzene interface. This phospholipid was found to lower markedly the surface tension by forming a stable monolayer when the interface was polarized so that the aqueous phase had a negative potential with respect to the nitrobenzene phase [50,51] (cf. Fig. 5). 

Figure 6. Dependence of transmembrane potential on abrupt changes of pH caused by equal additions of concentrated NaOH solution on both sides of a bilayer made from phosphatidylethanolamine (1, 3), containing residues of unsaturated fatty acids, dipalmitoyllecithin (2) containing saturated hydrocarbon chains.56 Curve (3) was obtained in an argon atmosphere. In all cases NADP in the concentration of 2.7 x IO-3 M was present on one side of the membrane. The experiment was conducted in the presence of IO-6 M TTFB.

Although phosphatidylserine is in general asymmetrically distributed in cell membranes with the bulk of this lipid in the cytoplasmic leaflet of the bilayer, some phosphatidylserine appears to reside in the outer lipid monolayer of the axonal membrane. Furthermore, this phosphatidylserine is involved in the nerve action potential. Treatment of an axon with extracellular serine decarboxylase converts phosphatidylserine to -ethanolamine, which results in a decrease in the action potential spike height. Catalysis of the reversed reaction by this enzyme in the presence of excess L-serine converts phosphatidylethanolamine to -serine. This produces an average of 28% increase in the action potential amplitude. It is worth noticing that several anaesthetic compounds have been shown to bind phosphatidylserine in vitroThe role of phosphatidylserine phase behavior in the nerve action potential will be discussed in somewhat more detail in Section 7. 

---