Fig. 2
From: A conserved odorant binding protein is required for essential amino acid detection in Drosophila
Binding properties of OBP19b with a competitive fluorescent assay. The fluorescent displacement of the fluorescent probe NPN by various taste compounds was evaluated by adding aliquots of 50 mM ligand (dissolved in 50 mM sodium phosphate buffer at pH 7.5) to final concentration ranging from 0 to 20 mM. a Fatty acid esters and bitter compounds were tested at a final concentration of 40 µM. b Amino acids, vitamins, acids, amines, trigeminal (isothiocyanate), and sugars compounds were tested at a 15 mM final concentration. c Fluorescent displacement of 20 l-amino acids, including l-phenylalanine (l-Phe: magenta color), l-glutamine (l-Gln: green) and l-alanine (l-Ala: cyan); three nonproteinogenic amino acids l-ornithine (l-Orn), l-canavanine (l-Can), l-citrulline (l-Cit); and three d-amino acids (d-phenylalanine: orange, d-glutamine: blue, and d-alanine: gray). Dots indicate essential amino acids. Statistical differences were determined using one-way ANOVA followed by Dunnett’s test (***p < 0.001; **p < 0.01). d Competitive-binding curves of l-Phe and l-Gln (showing the lowest Kdapp), l-Ala (negative control), and their three corresponding d-isomers. Data values represent the mean ± SEM. N = 4–13.
