Activation Of Pectate Lyase From Erwinia-Carotovora Subsp Atroseptica By Potato-Tuber Tissue-Extract

Tuber sap extract of three potato cultivars (Record, Maris Bard and Morene) activated endopectate lyase (PL) of Erwinia carotovora subsp. atroseptica by 50-84%. Addition of sap to the PL reaction mixture had no effect on Ca 2+ concentration nor on pH. Ability to activate was unaffected by boiling the sap extract but was lost following dialysis. The activating factors in cv. Record tuber sap extract were identified by TLC as galacturonic acid and glucuronic acid. Both carbohydrates activated PL by approximately 30% but were effective only in the range of 14·1 to 141·0 μg ml -1 in the PL reaction mixture. Kinetic studies of PL showed that whereas V max was not affected, K m values were reduced when tuber sap extract or the activating carbohydrates were added to the PL reaction mixture. The two carbohydrates apparently behaved as allosteric activators for PL. Allosteric activation of PL, which is an inducible enzyme, could be important in the early stages of infection.