Effect of Zn2+ on interfacial behaviour of diacylglycerol pyrophosphate and their mixtures with phosphatidic acid at the air-water interface

A.L. VILLASUSO, N. WILKE, B. MAGGIO Y E. MACHADO

Congreso; XXXVIII Reunión anual de la Sociedad Argentina de Biofísica; 2009

Diacylglycerol pyrophosphate (DGPP), a phosphorylated form of phosphatidic acid (PA) foundin plants and yeast but not in mammals, is a minor lipid that accumulates transiently undervarious abiotic stresses and during biotic interactions. DGPP formation may attenuate PAcontent but DGPP itself might be a signalling lipid. Zinc (Zn2+) is an essential mineral, servingas a cofactor for a variety of enzymes. Although not demonstrated in vivo, it has been shownthat Zn2+ can associated to DGPP.In this work we studied the interfacial behavior of DGPP and their mixture with palmitoyl oleoylphosphatidic 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 subfasesand that mixed monolayers of both lipids form non ideal mixtures, homogeneous at themicroscopic level (0.06 μm2). The interaction among these lipids leads to a diminution of themean molecular area and to an increase of the compressibility at all lateral pressures with anegative excess free energy of compression.In the presence of Zn2+, the pure lipids monolayers become more condensed with a moleculararea reduction of about 15% at low lateral pressure; by contrast, the surface behaviour of mixedmonolayers is not affected by Zn2+.The experiments suggest that Zn2+ interacts with the pure lipid monolayers, confirming thatDGPP interacts with Zn2+ in model systems. Converselly, in the mixed monolayers the lipids arequite closely packed and Zn2+ appears not capable of affecting the intermolecular packing.