Enzymes groups pectic

The plant cell wall contains different types of polysaccharides, proteins (structural glycoproteins and enzymes), lignin and water, as well as some inorganic components (1, 14-16). The plant cell suspensions, however, grow as a population of cells with a primary cell wall(17). The main components of these walls are cellulose-free polysaccharides and pectic polysaccharides in particular, which constitute 1/3 of their dry weight. (18). Some fragments, e g. methanol, acetic, ferulic and p-cumaric acids, are connected with the pectic polysaccharides by ester bonds with the carboxylic and hydroxylic groups. 

The group of pectic enzymes includes pectinesterase, which catalyzes the de-esterification of pectin, and depolymerizing enzymes which catalyze the splitting of glycosidic a-( 1 — 4) bonds of the D-galacturonan chain of the pectin molecule. 

There is the further, although remote, possibility that the only substantial variation in the composition of pectinic acids obtained from fruits and beets, and from some other sources, might be the result of differences in the occurrence in these of natural enzymes acting upon pectic substances. Pectinic acids isolated from beets have been shown to contain acetyl groups,8 the mode of attachment of which to the poly-... 

Assays for PE. Because PE hydrolyzes pectin to pectic acid and methanol, the enzyme concentration can be assayed by measuring the rate at which free carboxyl groups or methanol is released from the substrate. Kertesz (18) titrated the free carboxyl groups as they were formed by the action of the enzyme on pectin. He used methyl red to indicate the pH (6.2) and added 0.1N NaOH at frequent intervals to maintain the pH relatively constant for 30 min. The pH meter replaced the use of indicators in subsequent modifications (17, 19). Current procedures use automatic pH titrators to titrate alkali at constant pH (25). A blank is used to correct for the consumption of alkali due to its reaction with atmospheric CO2, or the reaction solution is protected from C0 with a blanket of N2. 

Pectic enzymes are defined and classified on the basis of their action toward the galacturonan part of the pectins. Two main groups are distinguished pectin methylesterases (pectin esterase, PE EC 3.1.11.1), which split off methoxy groups from pectin, transforming... 

A third group of hydrolytic enzymes specific for highly methylated pectins (polymethylgalacturonase, EC 3.2.1.41) has been described particularly in the older literature prior to the discovery of the pectin lyase by Albersheim et al. (21). We have never been able to find either exo-PL nor endo- and exo-PMG in our extensive screening of commercial preparations and micro-organisms. Many authors now agree that enzymes described as endo-or exo-PMG may very well have been a combined PE-PG activity, or a PL activity or even PG activity alone in cases where only initial velocities were measured. Extensive reviews of pectic enzymes have been published (22-26). 

There are several groups of pectic enzymes, including pectinesterase, the enzyme that hydrolyzes methoxyl groups, and the depolymerizing enzymes polygalacturonase and pectate lyase. 

Lao, C., Lopez-Tamames, E., Lamuela-Raventos, R. M., Buxaderas, S., Torre-Bonat, M. C. (1996). Effect of grape pectic enzyme treatment on phenolics of white musts and wines. In J. Vercauteren, C. Cheze, M. C. Dumon, J. F. Weber (Eds.), Polyphenols communications 96/XVII-Ith International Conference on Polyphenols (Vol. 2, pp. 303-304). Bordeaux Secretariat du Groupe Polyphenols. 

More recently another group of pectic enzymes has been described which degrade oligogalacturonides in preference to the longer chain molecules of polygalacturonic acid. In one study the attack rate was inversely proportional to chain length (50). The mechanism, as with... 

A second group of endo pectin lyases is characterized by optimum activity at slightly basic pH and by the ability to degrade polygalac-turonic acid (even though pectin is still favored). Sherwood 129) isolated this type of pectin lyase from Rhizoctonia solani. The enzyme had an optimal activity at pH 7.2 and degraded pectin faster than pectic acid. Bateman 128) found two pectin lyases from this microorganism which, when purified, were stimulated by cations and inhibited by EDTA. Optimal activity was between pH 8.0 and 9.0. 

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