Although this indicates a lower affinity than phosphoprotein antibodies the steep initial slope of the binding curve indicate presence of sites with higher affinity. Even more striking were the MIPs binding performance in the pH 7.4 buffer. In spite of the slightly lower affinity, the binding specificity shown by all phosphopeptide MIPs was absolute. For instance, the pYY MIP bound the pYY peptide but showed complete rejection of the YpY peptide and vice versa (Fig. ). To investigate whether the pronounced discrimination prevailed in complex matrices we went on to peptide enrichment tests.