Polygalacturonase Inhibiting proteins (PGIPs) are one of a plants first lines of defense against fungal attack. PGIPs are found in the plant cell wall and work to both inhibit the destruction caused by phytopathogenic fungal enzymes know as polygalacturonases (PGs), and to regulate the activity of these enzymes. Once secreted by the attacking fungi, PGs break through the plants polysaccharide rich cell wall allowing for penetration of the plant tissue by the fungi. PGIPs help defend the plant by binding to the PGs therefore regulating their activity, and permitting for the induction of defense elicitors. Through the use of surface plasmon resonance - biomolecular interaction analysis and mass spectrometry it is possible to study the specific interactions of PGIPs with PGs and identify PGIPs contained in a particular plant.