Pectate lyase, depolymerizing enzymes

Erwinia chrysanthemi, interest in the maceration process has led to the cloning and sequencing of four separate genes coding for different secreted pectate lyases (18,19), The production of these enzymes, either by the parent organism, or as recombinant enzymes in E. coli, has now led to their detailed characterization with respect to depolymerization mechanism. 

Figure 6. HPLC kinetics of polygalacturonic acid depolymerization by extracellular pectate lyases from crude supernatants of Erwinia chrysanthemi and Lachnospira multiparus cultures. A panels are full scale representations of products found over the reaction time sequence. B panels have expanded ordinates to better demonstrate the kinetics of minor products. Area unit refers to integration from HPLC tracings of product absorbance at 235 nm. Numbers in the panels refer to the degree of polymerization for individual products. Conditions for enzyme assay and product detection were the same as described for Figure 5.

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. 

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

All catalyze depolymerization by a beta-elimination reaction like that which occurs during base-catalyzed depolyraerization. Pectin lyases, all of which are endo-enzymes, catalyze beta-eliminations at esterified D-galacturonlc acid units (See Figure 1) (68). Pectate lyases catalyze beta-eliminations at nonesterifled D-galacturonic acid units. Both exo- and endo-pectate lyases are T[Pg.10]

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