Structures of ligands of R. prolixus lipocalins and the results of ITC analysis of tryptamine binding to ABP. (a) Structures of ligands known to bind to ABP. (b) Results of ITC analysis of tryptamine binding to ABP. Top, measured heats as a function of time. Bottom, individual binding enthalpies calculated by integration of raw data as a function of ligand:protein molar ratio. Squares represent the enthalpy per injection, while the solid line represents the result of fitting to a single-site binding model. Parameters: ΔH = −12.0 ± 0.2 kcal mol−1, Kassoc = (2.7 ± 0.3) × 106 M−1, TΔS = −3.06 kcal mol−1, N = 1.12 ± 0.01 molecules ligand bound per protein molecule. 1 cal = 4.186 J.