Studies on the Transport of l-Tyrosine into an Adrenergic Clone of Mouse Neuroblastoma

Studies on the transport of l-[U-14C]tyrosine into cultured mouse neuroblastoma clone N1E-115, which has high levels of tyrosine hydroxylase (EC 1.14.16.2), are presented. This transport was by a saturable process, exhibited marked exchanging properties, and was inhibited by a reagent which attacks sulfhydryl groups but not by metabolic inhibitors. No major ion requirements were found for this transport, which was sensitive to changes in temperature but not to changes in pH in the range of 6 to 8. Molecules with close structural analogy to l-tyrosine such as l-3,4-dihydroxyphenylalanine, l-3-iodotyrosine, and l-phenylalanine were potent competitive inhibitors of this transport with inhibitor constants (Ki) in the range of 2 to 6 x 10-5 m. In addition, compounds such as l-isoleucine, l-leucine, l-methionine, and l-valine caused inhibition of l-tyrosine transport. These results are consistent with the conclusion that l-tyrosine transport into this clone is by facilitated diffusion and by a mechanism similar to the leucine-preferring system which has been described by others.