Occurrence and Properties of Polygalacturonase in Avena and Other Plants

Polygalacturonase activity has been detected in a number of plants including seedlings of Phaseolus vulgaris, Zea mays, Avena sativa, and Pisum sativum. Particular emphasis was placed on characterizing the enzyme from oat seedlings. This enzyme is solubilized by 0.2 m NaCl, and its activity is highest near the apical tips of oat coleoptiles. It has a pH optimum between 5 and 5.5 and is activated by Ca(2+), with an optimal concentration of 0.4 mm. Cd(2+) also activates the enzyme but less effectively than Ca(2+). The rate of attack is maximal for substrates with chain lengths of about 20 units and slowest for digalacturonate. The oat enzyme hydrolyzes galacturonans by removing galacturonic acid units from the nonreducing ends and progressively shortens the substrate chains.