Valinomycin-induced potassium and rubidium permeability of intact cells of Acholeplasma laidlawii B

Membrane lipid, not polarized water, is responsible for the semipermeable properties of living cells

“…Dr. Ling is apparently unaware of a group of papers published in the last five years which directly address the question of whether or not the lipids of the plasma membrane function as the major nonelectrolyte permeability barrier in intact cells (35)(36)(37)(38)(39)(40). In these studies the fatty acid composition and cholesterol content of the membrane lipids of the simple procaryote Acholeplasma laidlawii B were systematically altered and the rates at which a number of nonelectrolytes passively diffuse into intact cells and into liposomes (closed, spherical lipid bilayer membranes) prepared from the total membrane lipid were measured at a variety of temperatures.…”

“…The permeabilities of intact cells and derived liposomes are markedly dependent on the chemical structure and chain length of the membrane lipid fatty acids. The incorporation of branched-chain or unsaturated fatty acids, or fatty acids of reduced chain length, increases nonelectrolyte permeability to a similar extent in both cells and liposomes (35,(37)(38)(39)(40). The nonelectrolyte permeability of both the plasma and liposomal membranes is reduced by the incorporation of cholesterol (35, 38-40).…”

“…In contrast to permeation rates, which are dependent on both permeant structure and membrane lipid composition, apparent activation energy values for the overall permeation process are dependent only on permeant structure and are not significantly affected by variations in the fatty acid composition or cholesterol content of the artificial or biological membrane systems (35,36,39). The permeability of intact cells and derived liposomes is a function of the fluidity of the membrane lipids as measured by their thermotrophic gel to liquidcrystalline membrane lipid phase transition temperatures (39,40). A. laidlawil B is equipped with a mechanism to control the fatty acid composition of its membrane lipids, and thus the fluidity and permeability of its plasma membrane, within certain limits (37).…”

Osmotic behaviour of acholeplasma laidlawii B cells with membrane lipids in liquid-crystalline and gel state

“…Since the lipid composition of the membranes of Acholeplasma laidlawii B can be varied considerably by changes in the growth medium [1], this organism was chosen for many studies on the significance of membrane lipid composition for the membrane functions [2][3][4][5][6]. Furthermore, the cells behave as osmometers with selectively permeable membranes and in comparative experiments conclusions on relative permeabilities have been drawn from the initial swelling rates in isotonic solutions which can be measured optically [2][3][4][5].…”

Επιβιωση Του Mycoplasma Hominis Στην Θερμοκρασια Του Περιβαλλοντος

“…1978, Slutzky et al 1977, δηλαδή άπό τό κλάσμα τών λιποπρωτεΐνών πού χαρακτηρίζεται άπό την υψηλότερη αναλογία χοληστερόλης προς τά φωσφολιποειδή. Σήμερα ή επικρατέστερη άποψη γιά τή σημασία της χοληστερόλης είναι δτι ρυθμίζει τή ρευστότητα (fluidity) τής κυτταροπλασματικής μεμβράνης,ανάλογα μέ τις συνθήκες τοϋ περιβάλλοντος οϋτως ώστε όλες οι λιπαρές ουσίες τής μεμβράνης νά βρί σκονται πάντοτε σέ ρευστή κατάσταση γιατί τότε παρουσιά ζεται ή άριστη διαπερατότητα τής μεμβράνης (Van der Neut-Kok et al 1974, Van Zoelen et al 1975.…”