THE DEPENDENCE OF THE LIPID BILAYER MEMBRANE: BUFFER PARTITION COEFFICIENT OF PENTOBARBITONE ON pH AND LIPID COMPOSITION

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Abstract
1 The membrane/buffer partition coefficient of [14C]-pentobarbitone has been determined as a function of the lipid composition of bilayer membranes. 2 A new technique based on ultrafiltration gave comparable results to conventional techniques but required less time for equilibration. 3 The membrane/buffer coefficient was independent of pentobarbitone concentration in the range studied. 4 The apparent partition coefficient varied with pH and was a linear function of the degree of dissociation of pentobarbitone. 5 Both the charged and uncharged forms of pentobarbitone partitioned into the membrane, the latter to a much greater extent than the former. 6 At low pH the highest partition coefficient observed was in egg phosphatidylcholine bilayer membranes. 7 Incorporation of cholesterol or phosphatidic acid into phosphatidylcholine membranes greatly reduced the partition coefficient. 8 High pressures do not greatly change these partition coefficients.