PubMed · 7495581
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1995. Membrane permeability.. https://doi.org/10.1016/0955-0674(95)80018-2
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A stochastic model for migration dynamics of solute molecules from the bulk aqueous phase to the intravesicular water pool is developed with a goal to interpret recent passive permeability measurements of bilayer membranes. Previously neglected fluctuations of the number of solubilized species in the inner water pool of a vesicle are naturally incorporated into the model. For a homogeneous one-phase bilayer, the model predicts exponential long-time asymptotics of the migration dynamics with a rate constant given by a sum of the frequencies of exit and entry of a solute molecule from/into the intravesicular water pool into/from the bulk aqueous phase. The long-time constant is directly related to the membrane permeability.
(1) The inhibition constant of L-sorbose flux from fresh human erythrocytes by D-glucose, Ki(sorbose) increases on cooling from 50 degrees C to 30 degrees C from 5.15 +/- 0.89 mM to 12.24 +/- 1.9 mM; the Ki(sorbose) of D-mannose increases similarly, indicating that the process is endothermic. (2) The activation energy Ea(sorbose) of net L-sorbose exit is 62.9 +/- 3.1 kJ/mol; in the co-presence of 5 mM D-glucose Ea(sorbose) is reduced to 41.7 +/- 1.6 kJ/mol (P < 0.005). (3) Cooling from 35 degrees C to 21 degrees C decreases the Ki(inf, cis) of auto-inhibition of D-glucose net exit from 5.2 +/- 0.3 mM to 1.36 +/- 0.06 mM; the Ki(inf, cis) of D-mannose falls from 10.9 +/- 1.65 mM to 5.7 +/- 0.3 mM. (4) The activation energy of D-glucose zero-trans net exit is 34.7 +/- 2.1 kJ/mol and that of D-mannose exit is 69.4 +/- 3.7 kJ/mol (P < 0.0025). (5) The exothermic and exergonic processes of auto-inhibition of D-glucose net exit are larger than those for D-mannose (P < 0.03). These data are consistent with D-glucose binding promoting an activated transporter state which following dissociation transiently remains; if an L-sorbose molecule binds within the relaxation time after D-glucose dissociation, it will have a higher mobility than otherwise. Cooling slows the relaxation time of the activated state hence raises the probability that L-sorbose will bind to the glucose-activated transporter. D-Glucose donates twice as much energy to the transporter as D-mannose, consequently produces more facilitation of flux. This view is inconsistent with the alternating carrier model of sugar transport in which net flux is considered to be rate-limited by return of the empty carrier, but is consistent with fixed two-site models.
The control of gene transcription by antigene oligonucleotides rests upon the specific recognition of double-helical DNA by triplex-forming oligonucleotides. The development of the antigene strategy requires access to the targeted DNA sequence within the chromatin structure of the cell nucleus. In this sudy we have used HIV-1 chronically infected cells containing the HIV provirus as endogenous genes to demonstrate that the integrated HIV-1 proviral genome is accessible to triplex-forming oligonucleotides within cell nuclei. An oligonucleotide-psoralen conjugate targeted to the polypurine tract (PPT) of the HIV-1 proviral sequence was used as a tool to convert the noncovalent triple-helical complex into a covalent lesion on genomic DNA after UV irradiation of cells. Triplex-derived adducts were analyzed using two different methods. The photo-induced psoralen cross-link prevented cleavage of the target sequence by DraI restriction endonuclease, and the sequence-specific inhibition of cleavage was revealed and quantitated by Southern blot analysis. A quantitative analysis of cross-linking efficiency was also carried out by a competitive PCR-based assay. These two approaches allowed us to demonstrate that a triplex-forming oligonucleotide can recognize and bind specifically to a 15-bp sequence within the chromatin structure of cell nuclei.