Permeability of small nonelectrolytes through lipid bilayer membranes

Abstract

Diffusion of small nonelectrolytes through planar lipid bilayer membranes (egg phosphatidylcholine-decane) was examined by correlating the permeability coefficients of 22 solutes with their partition coefficients between water and four organic solvents. High correlations were observed with hexadecane and olive oil (r = 0.95 and 0.93), but not octanol and ether (r = 0.75 and 0.74). Permeabilities of the seven smallest molecules (mol wt less than 50) (water, hydrofluoric acid, hydrochloric acid, ammonia, methylamine, formic acid and formamide) were 2- to 15-fold higher than the values predicted by the permeabilities of the larger molecules (50 less than mol wt less than 300). The "extra" permeabilities of the seven smallest molecules were not correlated with partition coefficients but were inversely correlated with molecular volumes. The larger solute permeabilities also decreased with increasing molecular volume, but the relationship was neither steep nor significant. The permeability pattern cannot be explained by the molecular volume dependence of partitioning into the bilayer or by the existence of transient aqueous pores. The molecular volume dependence of solute permeability suggests that the membrane barrier behaves more like a polymer than a liquid hydrocarbon. All the data are consistent with the "solubility-diffusion" model, which can explain both the hydrophobicity dependence and the molecular volume dependence of nonelectrolyte permeability.

Design of artificial cell–cell communication using gene and metabolic networks

“…(i) The system is a well mixed homogenous culture. (ii) Acetic acid but not acetate transport across the cell membrane is relevant, because the membrane permeability of acetic acid (P m , 6.9⅐10 Ϫ4 cm͞s) is about three orders of magnitude higher than that of acetate (25,26). The influence of ⌬pH on acetate concentration inside and outside of the cells was simulated (Fig.…”

110 Years of the Meyer–Overton Rule: Predicting Membrane Permeability of Gases and Other Small Compounds

“…(4)]: (4) This means that τ is equal to only about 1/100 of the time required for mixing the solutions, even in the best stopped-flow devices currently available on the market. In other words, investigation of SA transport by stopped flow is impossible.…”

“…[4][5][6][7][8] All the exceptions to this rule, which have been reported so far, can be divided into two groups:…”

Molecular determinants of ammonia and urea conductance in plant aquaporin homologs

“…Another NH 3 passed the membrane lipids, suggesting that pure POPE membranes still let some ammonia through. Taking into account the well-established intrinsic background permeability of lipid membranes to NH 3 [15], it remains questionable whether PIP aquaporins can thus enhance the flux across native membranes (see Section 3).…”