Polygalacturonic acid, properties

ViUemez, C.L., Swanson, A.L., and Hassid, W.Z. (1966) Properties of a polygalacturonic acid-synthesizing enzyme system from Phaseolus aureus seedlings. Arch.Biochem.Biophys. 116 446-452. 

Saprophytic anaerobic bacteria, e.g. the ruminant bacterium Lachnospira multiparus and the methane digestor isolate, Clostridium populeti, secrete only acidic pectate lyases that exhibit an exolytic/endolytic depolymerization toward polygalacturonate. It will be important to determine if this acidic property contributes to the adsorption of these enzymes to the secreting bacterium, perhaps contributing to the efficiency with which the bacteria are able to assimilate the products generated by these enzymes. 

The reaction conditions chosen for the assays are based on published optimal conditions for PGase enzymes. These enzymes typically have maximal activities at slightly acidic pH (Tucker and Seymour, 2002) and, in general, appear to be relatively stable at temperatures from 30° to 40°C. Optimal reaction conditions are likely to be enzyme specific, so one may have to alter the conditions to match the properties of the enzyme of interest. In all cases, the analyst should take into account the properties of the substrate, particularly its solubility, as well as the properties of the enzyme. For example, because solutions of polygalacturonic acid tend to gel as the pH is lowered below 3, viscometric assays (Basic Protocol 2) at these relatively low pHs are often not feasible. 

Pectic and Polygalacturonic Acids.—The effects of cross-linking of pectic acid on the cation-exchange properties, on the binding of endo-polygalacturonase, and on the biodegradability have been examined. ... 

Pectinic acids form viscous solutions and show the typical properties of macromolecular polysaccharides. Pectinic acids are susceptible to thermal and oxidative degradation and to the effect of alkali. The latter saponify the methyl ester groups and also affect the polygalacturonic acid structure in some not clearly understood manner. 

Pectin belongs to a family of plant polysaccharides in which the polymer backbone consists of (1— 4)-linked a-D-galacturonic acid repeating-units. Often, (1— 2)-linked a-L-rhamnose residues interrupt the regular polygalacturonate sequence. The high viscosity and gelling properties of pectins are exploited by the food and pharmaceutical industries. X-Ray studies on sodium pectate, calcium pectate, pectic acid, and pectinic acid (methyl ester of pectic acid) have disclosed their structural details. 

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