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Physiology and Biochemistry

Pectic Enzyme Complex from Erwinia carotovora: A Model for Degradation and Assimilation of Host Pectic Fractions. J. P. Stack, Graduate research assistant, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; M. S. Mount(2), P. M. Berman(3), and J. P. Hubbard(4). (2)(3)Associate professor, research assistant, respectively, Department of Plant Pathology, University of Massachusetts, Amherst 01003; (4)Graduate research assistant, Department of Seed and Vegetable Sciences, New York Agricultural Experiment Station, Geneva 14456. Phytopathology 70:267-272. Accepted for publication 5 September, 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-267.

The intracellular pectic enzyme complex of Erwinia carotovora (Isolate 14) is comprised of at least four 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 has the ability to depolymerize a sodium polypectate substrate in both an endo-lyase manner at pH 8.5 in the presence of Ca++, and in an endo-hydrolase manner at pH 6.0 in the presence or absence of divalent cations. To date the two 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 (5.510.0), with optimal activity at pH 8.5. PD II, which also exhibits limited endo-like activity, requires Mn++ for optimal activity, while PD III is enhanced by, but not dependent upon, divalent cations for activity. PDIV (pI 6.5), an oligogalacturonide lyase, converts unsaturated dimer and other oligouronides to, primarily, unsaturated monomer at pH 7.58.5 and to, predominately, d-galacturonic acid at pH 6.0. PD 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.