Fungal polygalacturonases exhibit different substrate degradation patternsand differ in their susceptibilities to polygalacturonase-inhibiting proteins

Polygalacturonic acid (PGA) was hydrolyzed by polygalacturonases (PGs) puri fied from six fungi. The oligogalacturonide products were analyzed by HPAEC -PAD (high performance anion exchange chromatography-pulsed amperimetric de tection) to assess their relative amounts and degrees of polymerization, Th e abilities of the fungal PGs to reduce the viscosity of a solution of PGA were also determined. The potential abilities of four polygalacturonase-inh ibiting proteins (PGIPs) from three plant species to inhibit or to modify t he hydrolytic activity of the fungal PGs were determined by colorimetric an d HPAEC-PAD analyses, respectively. Normalized activities of the different PGs acting upon the same substrate resulted in one of two distinct oligogal acturonide profiles. Viscometric analysis of the effect of PGs on the same substrate also supports two distinct patterns of cleavage. A wide range of susceptibility of the various PGs to inhibition by PGIPs was observed. The four PGs that were inhibited by all PGIPs tested exhibited an endo/exo mode of substrate cleavage, while the three PGs that were resistant to inhibiti on by one or more of the PGIPs proceed by a classic endo pattern of cleavag e.