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Metabolism and Enzymology

Uronic Acid Products Release from Enzymically Active Cell Wall from Tomato Fruit and Its Dependency on Enzyme Quantity and Distribution ¹

Vegetable Crops Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida 32611

Isolated cell wall from tomato (Lycopersicon esculentum Mill. cv Rutgers) fruit released polymeric (degree of polymerization [DP] > 8), oligomeric, and monomeric uronic acids in a reaction mediated by bound polygalacturonase (PG) (EC 3.2.1.15). Wall autolytic capacity increased with ripening, reflecting increased levels of bound PG; however, characteristic oligomeric and monomeric products were recovered from all wall isolates exhibiting net pectin release. The capacity of wall from fruit at early ripening (breaker, turning) to generate oligomeric and monomeric uronic acids was attributed to the nonuniform ripening pattern of the tomato fruit and, consequently, a locally dense distribution of enzyme in wall originating from those fruit portions at more temporally advanced stages of ripening. Artificial autolytically active wall, prepared by permitting solubilized PG to bind to enzymically inactive wall from maturegreen fruit, released products which were similar in size characteristics to those recovered from active wall isolates. Extraction of wall-bound PG using high concentrations of NaCl (1.2 molar) did not attenuate subsequent autolytic activity but greatly suppressed the production of oligomeric and monomeric products. An examination of water-soluble uronic acids recovered from ripe pericarp tissue disclosed the presence of polymeric and monomeric uronic acids but only trace quantities of oligomers. The significance in autolytic reactions of enzyme quantity and distribution and their possible relevance to in vivo pectin degradation will be discussed.

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				J.-P. Chun and D. J. Huber Polygalacturonase-Mediated Solubilization and Depolymerization of Pectic Polymers in Tomato Fruit Cell Walls . Regulation by pH and Ionic Conditions Plant Physiology, August 1, 1998; 117(4): 1293 - 1299. [Abstract] [Full Text]