Effect of the polygalacturonase inhibitor from pea on the hydrolysis of pea cell walls by the endopolygalacturonase from Ascochyta pisi

Exo–polygalacturonase (exo–PG) and endo–PG from Ascochyta pisi rapidly adsorbed to insoluble fragments of cell walls from pea leaflets as did the endo–PG inhibitor that was isolated from these organs. The wall fragments were hydrolysed by the exo– and endo–PG but the rates were, respectively, only 1–8 and 8% of the rate of hydrolysis of soluble polygalacturonic acid (PGA). Although the endo–PG inhibitor rapidly and completely inhibited the hydrolysis of soluble PGA by the endo–PG it had no effect on the rate of hydrolysis of pea cell wall fragments by this enzyme. Extracts of the intercellular fluid from pea leaflets contained only 4% of the inhibitor present in that organ and the remainder was presumably intracellular. These findings indicate that the endo–PG inhibitor may be less effective in vivo than was previously suspected.