CONICET | Buscador de Institutos y Recursos Humanos

Diacylglycerol pyrophosphate (DGPP), a phosphorylated form of phosphatidic acid (PA) found in plants and yeast but not in mammals, is a minor lipid that accumulates transiently under various abiotic stresses and during biotic interactions. DGPP formation may attenuate PA content but DGPP itself might be a signalling lipid. Zinc (Zn2+) is an essential mineral, serving as a cofactor for a variety of enzymes. Although not demonstrated in vivo, it has been shown that Zn2+ can associated to DGPP. In this work we studied the interfacial behavior of DGPP and their mixture with palmitoyl oleoyl phosphatidic acid (PA) at the air-water interface at pH 8 (both lipids are negativelly harged) with and without ZnCl2. It was previously shown that DGPP and POPA form expanded monolayers on NaCl subfases and that mixed monolayers of both lipids form non ideal mixtures, homogeneous at the microscopic level (0.06 mm2). The interaction among these lipids leads to a diminution of the mean molecular area and to an increase of the compressibility at all lateral pressures with a negative excess free energy of compression. In the presence of Zn2+, the pure lipids monolayers become more condensed with a molecular area reduction of about 15% at low lateral pressure; by contrast, the surface behaviour of mixed monolayers is not affected by Zn2+. The experiments suggest that Zn2+ interacts with the pure lipid monolayers, confirming that DGPP interacts with Zn2+ in model systems. Converselly, in the mixed monolayers the lipids are quite closely packed and Zn2+ appears not capable of affecting the intermolecular packing.