Abstract: The invention provides in a first aspect a method for the identification of an ZAP-70 interacting compound, comprising the steps of a) providing a protein preparation containing phosphorylated ZAP-70, b) contacting the protein preparation with aminopyrido-pyrimidine ligand 24 immobilized on a solid support under conditions allowing the formation of an aminopyrido-pyrimidine ligand 24—phosphorylated ZAP-70 complex, c) incubating the aminopyrido-pyrimidine ligand 24—phosphorylated ZAP-70 complex with a given compound, and d) determining whether the compound is able to separate phosphorylated ZAP-70 from the immobilized aminopyrido-pyrimidine ligand 24.

Abstract: The present invention relates to methods for the characterization of enzymes or of enzyme-compound complexes, wherein the enzyme is obtained from a protein preparation with the help of at least one broad spectrum ligand immobilized on a solid support and wherein the enzyme is characterized by mass spectrometry. These methods are useful for the screening of non-immobilized compound libraries, selectivity profiling of lead compounds and mechanism of action studies in living cells.