PubMed · 4696437
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G S Robertson, W F Hamilton. 1973. Methoxyflurane and renal function.. https://doi.org/10.1093/bja%2F45.1.55
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The effect of undecaprenyl phosphate (C55-P) on dioleoylphosphatidylcholine (DOPC) bilayer lipid membranes has been studied. The current-voltage characteristics, steady-state diffusion potentials, membrane conductance-temperature relationships, membrane electric capacitance and membrane breakdown voltage have been measured for different mixtures of undecaprenyl phosphate and DOPC. The ratio of permeability coefficients for sodium and chloride ions, the activation energy for ion migration across the membrane and membrane thickness have been determined. The electrical measurements showed that undecaprenyl phosphate decreases membrane-normalized conductance, membrane ionic permeability, membrane hydrophobic thickness and membrane selectivity for chloride ions, and increases the activation energy for ion transport, membrane nonlinearity potential, membrane specific capacitance, membrane electromechanical stability and membrane selectivity for sodium ions. From the results, we suggest that the interaction of the gradient of electric transmembrane potential with the negative charge of the phosphate group of C55-P determines the dynamics, conformation and aggregation behaviour of undecaprenyl phosphate in phospholipid membranes. Some implications of these findings for a possible regulation of the C55-P-dependent expression of polysialic acid capsule in Escherichia coli K1 bacterial cells are indicated.
The interactions of the three human embryonic haemoglobins with chloride ions have been investigated. Each of the three embryonic haemoglobins exhibits a unique pattern of oxygen-affinity-dependence on chloride ion concentration. Human embryonic haemoglobin Portland (zeta 2 gamma 2) is found to be completely insensitive to chloride ion concentration. Haemoglobin Gower I (zeta 2 gamma 2) shows a small concentration dependence, whilst haemoglobin Gower II (alpha 2 epsilon 2) exhibits a dependence approaching that of the adult protein. The degree of co-operativity for each protein is essentially chloride concentration independent. The chloride-dependent and -independent components of the alkaline Bohr effects have been measured for each of the embryonic haemoglobins and compared with that of the adult protein. Both the chloride-binding data and the Bohr effect have been analysed in terms of the recently developed allosteric model proposed by Perutz [Perutz, Fermi, Poyart, Pagnier and Kister (1993) J. Mol. Biol. 233, 536-545].