Pectic Enzyme Complex fromErwinia carotovora: A Model for Degradation and Assimilation of Host Pectic Fractions

Abstract

The intracellular pectic enyme complex of E. carotovora (Isolate 14) is comprised of at least 4 pectate depolymerases, PD I, PD II, PD III and PD IV. PD I, a single peak when isoelectric focused, has an isoelectric point (pI) of 9.4 and the ability to depolymerize a sodium polypectate substrate in both an endo-lyase manner at pH 8.5 in the presence of Ca2+, and in an endo-hydrolase manner at pH 6.0 in the presence or absence of divalent cations. To date the 2 activities of PD I enzyme(s) have been inseparable. PD I is the only pectic enzyme(s) that is found extracellularly. PD II (pI 8.0) and PD III (pI 6.3) exhibit exo-lyase activity over a broad pH range (5.5-10.0), with optimal activity at pH 8.5. PD II, which also exhibits limited endo-like activity, requires Mn2+ for optimal activity, while PD III is enhanced by, but not dependent upon, divalent cations for activity. PD IV (pI 6.5), an oligogalacturonide lyase, converts unsaturated dimer and other oligouronides to, primarily, unsaturated monomer at pH 7.5-8.5 and to, predominately, D-galacturonic acid at pH 6.0. RD IV also exhibits very limited exo-lyase and exo-hydrolase activity on sodium polypectate. A model describing the possible mode of action of the pectic enzyme complex in E. carotovora is presented.