PubMed · 8257612
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1993. Membranes.. https://pubmed.ncbi.nlm.nih.gov/8257612/
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We show that it is possible to produce phosphorylation difference maps of biological membranes under conditions which reflect those in vivo and in which proteins remain functional. We also demonstrate that absolute levels of phosphorylation are retrieved through the application of an appropriate calibration method. Finally we show that the kinetics of phosphorylation/dephosphorylation can also be monitored. These methods are demonstrated on photosynthetic membranes from higher plants, for which protein phosphorylation is the dominant regulatory mechanism. We show directly that the most recent estimates of the phosphorylation levels in this system are reasonably accurate. Phosphorylation difference maps show that the distribution of phosphates is not even, with significantly higher levels at the membrane margins and patches of high phosphate density next to patches of low charge density.
A mathematical description is presented of osmotic flows across both ideally semipermeable membranes and membranes permeable not only for the solvent but also for the solute. The principles of thermodynamics of irreversible processes used for the description are given and illustrated on the example of electroosmosis. Modern ideas about the physical basis of osmotic pressure on porous membranes are discussed and an experiment is described that models the processes of osmosis on a macroscopic level.
From seashells to DNA, chirality is expressed at every level of biological structures. In self-assembled structures it may emerge cooperatively from chirality at the molecular scale. Amphiphilic molecules, for example, can form a variety of aggregates and mesophases that express the chirality of their constituent molecules at a supramolecular scale of micrometres. Quantitative prediction of the large-scale chirality based on that at the molecular scale remains a largely unsolved problem. Furthermore, experimental control over the expression of chirality at the supramolecular level is difficult to achieve: mixing of different enantiomers usually results in phase separation. Here we present an experimental and theoretical description of a system in which chirality can be varied continuously and controllably ('tuned') in micrometre-scale structures. We observe the formation of twisted ribbons consisting of bilayers of gemini surfactants (two surfactant molecules covalently linked at their charged head groups). We find that the degree of twist and the pitch of the ribbons can be tuned by the introduction of opposite-handed chiral counterions in various proportions. This degree of control might be of practical value; for example, in the use of the helical structures as templates for helical crystallization of macromolecules.