Tolaasin is a lipodepsipeptide (lipo = hydrophobic side chain, depsipeptide is an amino acid ring closed in a particular way) produced by strains of Pseudomonas tolaasii, and it causes Brown Blotch disease in mushrooms. This is a major problem in commercial mushroom growing. Tolaasin is detected by the formation of a "white line" when it comes into contact with the lipodepsipeptides, WLIP (White Line Inducing Peptide) created by Pseudomonas reactans. WLIP is evidently antagonistic to tolaasin but the mechanism is not understood. White line formation is enhanced by the biogenic amine, octopamine. Preliminary reflection experiments confirm a strong specific interaction of octopamine and WLIP. This seems to require an unfolding of the known solid state structure of WLIP and we propose to determine the layer structure using reflectometry and part deuterated WLIP.