Negatively charged vesicles made of non-stoichiometric amounts of sodium dodecylsulfate and cetyltrimethylammonium bromide were characterised by physico-chemical methods. Interactions with lysozyme were examined by calorimetry. A remarkable heat effect is observed upon diluting the protein with the vesicular pseudo-solvent. The maximum Delta H-bind value occurs at complete vesicle charge neutralisation by the protein. (c) 2007 Elsevier B.V. All rights reserved.