A sodium- and potassium-stimulated tyrosine transporter from Leptinotarsa decemlineata midguts

Tyrosine transport across the midgut brush border membrane of Leptinotarsa decemlineata was characterized using brush border membrane vesicles (BBMV). The concentrations of tyrosine in potato foliage that are potentially available to the insect and the hemolymph tyrosine concentration were estimated. l-Tyrosine transport into BBMV is stimulated by SCN^- and Cl^- salts of K⁺ and Na⁺ under isosmotic conditions. Compared to ion-independent l-tyrosine transport, KSCN and NaSCN increased both the J_max and K_t for l-tyrosine uptake. Ion independent l-tyrosine uptake was strongly inhibited by leucine, phenylalanine, proline and serine and moderately inhibited by lysine, threonine, tryptophan and valine. The NaSCN stimulated tyrosine transporter was not affected by d-tyrosine and only cysteine inhibited uptake in the presence of NaSCN. This is the first report of ion-dependent amino acid transport in the Coleoptera and the first characterization of a tyrosine transporter in insects.