title: Absolute measurement of phosphorylation levels in a biological membrane using atomic force microscopy: the creation of phosphorylation maps.
abstract: 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.
authors.affiliation: Molecular Dynamics Group, Biological and Biophysical Chemistry Section, Department of Chemistry, Imperial College of Science Technology and Medicine, Exhibition Road, London SW7 2AZ, UK.
authors.forename: Je-Wen
authors.initials: JW
authors.lastname: Liou
authors.forename: Xavier
authors.initials: X
authors.lastname: Mulet
authors.forename: David R
authors.initials: DR
authors.lastname: Klug
mesh_terms: D008566:Membranes / Q000502:physiology*; D018625:Microscopy, Atomic Force / Q000379:methods; D010744:Phosphoric Monoester Hydrolases; D010766:Phosphorylation; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism; D018521:Plant Physiological Phenomena; D055672:Static Electricity
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D010744:Phosphoric Monoester Hydrolases