GluR23Y is a biological active peptide. (This GluR23Y peptide was used in ELISA cell-surface assay for the insulin-stimulated endocytosis of native AMPA receptors in cultured hippocampal neurons. GluR23Y prevented any insulin-induced reduction. The blockade of insulin action was observed when the GluR23Y peptide was delivered into neurons by fusing it to the membrane transduction domain of HIV-1.)