Amino AcidsAmino Acid Transport SystemsReceptors, Purinergic P2X1LeucineSequence Homology, Amino AcidAmino Acid SequenceAmino Acid SubstitutionCloning, MolecularAmino Acids, EssentialSequence AlignmentBase SequenceMutationAmino Acid MotifsEscherichia coliMolecular Sequence DataBinding SitesKineticsMutagenesis, Site-DirectedNeutral RedDNA, ComplementaryAmino Acids, AromaticSequence Homology, Nucleic AcidProtein ConformationPeptide FragmentsModels, MolecularRecombinant ProteinsAmino Acids, Branched-Chain