Modulation by small hydrophobic molecules of valinomycin-mediated potassium transport across phospholipid vesicle membranes

Journal Article · Thu Jan 01 04:00:00 EST 1981 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00509a020· OSTI ID:5301618

Clement, N R; Gould, J M

The effects of small hydrophobic molecules on valinonycin-mediated K/sup +/ transport in small unilamellar soybean phospholipid vesicles have been studied by using a vesicle-entrapped pH-sensitive hydropholic fluorescence probe to monitor counterion-limited, passive H/sup +/ diffusion into vesicles after an abrupt decrease in external pH. Under conditions where, even in the absence of valinomycin, transmembrane K/sup +/ movement represented the primary and limiting counterion flux, <1 valinomycin molecule/vesicle was sufficient to accelerate the rate of H/sup +/ entry into all of the vesicles. Incorporation of the bulkily substituted molecules butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), and p-di-tert-butylbenzene into soybean lipid bilayers had no effect upon K/sup +/ diffusion in the absence of valinomycin. However, the presence of these hydrophobic molecules increased the apparent efficacy for K/sup +/ transport of a given valinomycin concentration by as much as 4-6 fold. The less bulky membrane perturbants tert-butyl alcohol, phenol, and heptane showed very much less dramatic effects. While the rate of valinomycin-mediated K/sup +/ transport (in the presence or absence of BHT) was very sensitive to temperature-induced changes in membrane fluidity, the degree of synergistic interaction between valinomycin and BHT was independent of temperature. Furthermore, BHT, BHA, and p-di-tert-butylbenzene, at levels which alter valinomycin-mediated K/sup +/ transport, did not by themselves induce changes in membrane fluidity. It is postulated that changes in phospholipid head-group packing and/or surface charge density brought about by the presence of bulky perturber molecules leads to changes in partitioning of valinomycin or the valinomycin-K/sup +/ complex between the aqueous and membrane phases.

• Research Organization: Univ. of Notre Dame, IN
• OSTI ID: 5301618
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 20:6; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550200* -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
ALKALI METALS
ANTI-INFECTIVE AGENTS
ANTIBIOTICS
CELL CONSTITUENTS
CELL MEMBRANES
DRUGS
ELEMENTS
ESTERS
GLYCINE HISPIDA
INHIBITION
LEGUMINOSAE
LIPIDS
LIPOSOMES
MEMBRANE TRANSPORT
MEMBRANES
METALS
MODULATION
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
ORGANOIDS
PERMEABILITY
PH VALUE
PHOSPHOLIPIDS
PLANTS
POTASSIUM
SYNERGISM
VALINOMYCIN