Based on analysis of aligned amino acid sequences the following statem
ents are made: (i) There is evolutionary homology between the N-termin
al extracellular region of ionotropic Glutamate receptors/Kainate Bind
ing Proteins and a family of procaryote amino acid binding proteins. (
ii) Homology of the N-terminal extracellular domain of the metabotropi
c glutamate receptors with a family of receptors with a guanylate cycl
ase intracellular domain appears to be valid. (iii) There is no eviden
ce for homology between the N-terminal extracellular domain of the nic
otinic Acetylcholine, GABA, Glycine and 5HT3 receptors and that of the
ionotropic Glutamate receptors/Kainate Binding proteins. (iv) The pro
posal of homology for the N-terminal extracellular domain of metabotro
pic Glutamate receptors and that of ionotropic Glutamate receptors doe
s not appear to hold.