Purification and Characterization of an endo-Polygalacturonase from the Gut of West Indies Sugarcane Rootstalk Borer Weevil (Diaprepes abbreviatus L.) Larvae

An endo-polygalacturonase (PG) (EC:3.2.1.15) with a pI of 9.4 and an M_r of 44,500 was purified to electrophoretic homogeneity from the gut of West Indies sugarcane rootstalk borer weevil (Diaprepes abbreviatus L.) larvae. Hydrolytic activity was maximal in 150 mM sodium acetate, pH 5.5, at 30°C. Kinetic determinations yielded an apparent K_m of 3.68 mg polygalacturonic acid (PGA)/ml and a V_max of 283 μmol galacturonic acid/min/mg protein for PGA. Enzymatic activity was inhibited by a polygalacturonase inhibitor protein from “Hamlin” orange flavedo. The purified protein does not appear to be glycosylated, and its N-terminal sequence showed no homology to any PG protein sequences in data banks.