Glyceraldehyde-3-phosphate dehydrogenase from rabbit muscle can be adsorbed on charged lipid bilayers by electrostatic forces. Upon binding to phosphatidylinositol liposomes the enzyme modifies its conformational state as it is shown by resonance energy transfer experiments. In the presence of 2-mercaptoethanol o-phthaldialdehyde reacts with amino groups of the protein and the covalently bound fluorophore is an acceptor of excitation energy transferred from tryptophanyl residues of the protein. The observed decrease of energy transfer efficiency upon binding to phosphatidylinositol liposomes is compared with the influence of the urea on the fluorescence spectra of the labelled protein. Significance of conformational changes of the enzyme upon adsorption on liposomes in the regulating function of cell membranes is discussed.
