Biological membranes are a unique, chemically complex environment comprised of several components that are commonly mimicked by lipid bilayer vesicles. In effort to create a more complex, and therefore more realistic, description of biological membranes, two amino acids were added to lipid bilayer vesicles to determine how their presence altered the partitioning behavior of two structurally similar Coumarin solutes. Differential scanning calorimetry and time-resolved fluorescence spectroscopy were used to quantify the partitioning behavior of Coumarin 151 (C151) and Coumarin 152 (C152) into a DPPC lipid bilayer vesicle with the addition, separately, of L-Phenylalanine (L-PA) and N-Acetyl-DL-tryptophan (NAT). Results showed that the presence of L-Phenylalanine did not increase partitioning behavior when the solute, C151, does not have an initial affinity for partitioning. In the case of C152, the presence of L-phenylalanine inhibited partitioning into the gel phase of the lipid bilayer leaving more C152 in the surrounding PBS buffer. Of the C152 that did partition into the bilayer, L-PA enhanced accumulation in the bilayer’s hydrophobic region. When the lipid vesicle is in the liquid-crystalline phase of the lipid bilayer, the C152 fully partitioned into the bilayer in concentrations of up to 80% in the polar region created by DPPC’s glycero-backbones and hydrating water molecules. Addition of NAT to DPPC vesicle-containing solutions partitioning resulted in interesting C151 and C152 partitioning behavior not seen with L-PA or in the absence of amino acids. Partitioning in the DPPC/NAT system suggests that NAT itself interacts strongly with the DPPC bilayer and that C151 and C152 mitigate this amino acid-lipid interaction to form a more weakly bound complex that nevertheless remains associated with the lipid bilayer.

Effects of amino acids on coumarin partitioning in model biological membranes

ACS Spring Meeting 2021

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