An extracellular polygalacturonase [EC 126.96.36.199], named PG-543, was purified from the culture of Geotrichum candidum IEV 543, a phytopathogenic fungi isolated from infected lemon. The molecular mass of the enzyme was estimated to be 26 kDa by SDS-PAGE. The pH optimum determined was 5.5; the enzyme showed high stability in the pH range between 4.0 and 6.0. The temperature optimum was 37 ºC. Furthermore, a proteinaceous inhibitor of the polygalacturonase (PG) named PGIP was isolated from lemon albedo. This protein was able to maintain the inhibitory activity in a wide range of pH and temperature. The maximal interaction between PG-PGIP was reached after 20 min of contact. PGIP did not show toxic effect on Artemia salina in the concentration range that was active on PG enzyme. Also, the proteinaceous inhibitor did not show mutagenic nor phytotoxic effects.
Our results suggest that, the PGIP isolated from lemon could be used as a natural product to decrease the propagation of pathogenic fungi responsible for postharvest diseases in citrus by the inhibition of hydrolytic enzymes secreted by pathogens.