DESCRIZIONE
The present invention relates to a method of enriching or screening for one or more target molecules from a primary source, which method comprises to provide at least one peptidic ligand comprising at least one lysine (K) and immobilized to a solid support; contacting the ligand(s) with a primary source comprising at least one target molecule comprising glutamine (Q); allowing the formation of complexes between the ligand and the target molecule; and separating the complexes from the primary source. The target molecule(s) comprises glutamine, and step c is performed in the presence of a catalytic protein comprising transglutaminase (TG). The catalytic protein comprising transglutaminase (TG) may comprise transglutaminase originating from fish, such as Atlantic cod TG (AcTG), e.g. AcTG-1, and the primary source may include waste material from the fish or dairy industry.