Lyases pectin lyase

Immobilization. The fixing property of PEIs has previously been discussed. Another appHcation of this property is enzyme immobilization (419). Enzymes can be bound by reactive compounds, eg, isothiocyanate (420) to the PEI skeleton, or immobilized on soHd supports, eg, cotton by adhesion with the aid of PEIs. In every case, fixing considerably simplifies the performance of enzyme-catalyzed reactions, thus faciHtating preparative work. This technique has been appHed to glutaraldehyde-sensitive enzymes (421), a-glucose transferase (422), and pectin lyase, pectin esterase, and endopolygalacturonase (423). 

Other polysaccharides of primary cell walls.-A complex mixture of enzymes including endopolygalacturonase, pectin methylesterase, and/or pectin lyase solubilizes a mixture of polysaccharides from the primary cell walls of fruits [57-64]. Food scientists have referred for some 15 years to this mixture of polysaccharides as the hairy region to describe the highly branched character of the polysaccharides in the fraction and to emphasize the contrast to unbranched homogalacturonan. The recent discovery of rhamnogalacturonan hydrolase [65,66], which selectively cleaves the backbone of RG-I, led to the realization that the hairy... 

Bussink et al. [4] and Kusters-van Someren et al. [5] have shown that in A. niger for both polygalacturonases (PGs) and pectin lyases (PLs) families of genes are present seven... 

The discovery of these enzymes enables a better structural characterisation of the hairy (ramified) regions of pectin, as already demonstrated by Schols et al. (1990b) and also of native plant cell wall pectin (Schols et al., 1995). In this study we show how the two exo-enzymes of the above described series, the RG-rhamnohydrolase and the RG-galacturonohydrolase, can be used as tools in the characterisation of unknown RG fragments. These unknown fragments were the products of RG-hydrolase or RG-lyase action toward linear RG oligomers (RGO s), which were produced by acid hydrolysis of sugar beet pulp. 

Bartling, S., Wegener, C. and Olsen, O. (1995). Synergism between Erwinia pectate lyase isoenzymes that depolymerize both pectate and pectin. Microbiology 141,873-881. 

Erwinia chrysanthemi synthesizes and secretes a large number of pectinases. The major pectinases include a pectin methylesterase PemA and five isoenzymes of endo-pectate lyases PelA, PelB, PelC, PelD and PelE. In addition, secondary pectinases were identified a pectin methylesterase PemB, two endo-pectate lyases PelL and PelZ, an exo-pectate lyase PelX and an exopolygalacturonase, PehX. The regulation of pectinase synthesis is very complex and dependent on many environmental conditions. It is induced by pectin catabolic products and affected by growth phase, catabolite repression, osmolarity, iron or oxygen starvation... 

Structural analysis of the two pectate lyases PelC and PelE (5, 6), demonstrated that these proteins fold in a large heHx of parallel P strands. A stack of asparagine residues parallel to the helix probably plays a role in the stabUity of this structure. Identification of the structurally conserved amino adds lead to a reaHgnment of the protein sequences (7). In addition to Erwinia extracellular pectate lyases, the multiple aHgnment indudes the Bacillus subtilis pectate lyase, Aspergillus tdger and E. carotovora pectin lyases and plant proteins. 

Digestion of PGA by the PelL enzyme yielded a mixture of unsaturated ohgogalacturonides, giving evidence that PelL is an endo-deaving lyase (17). An exo-enz3mie, such as the EC 16 PelX, would generate a single product (15). The PelL protein differs from the major E. chrysanthemi pectate lyases in its ability to cleave both PGA and methylated pectin (17). The PelL activity has a basic optimum pH and an absolute requirement for Ca + ions. Analysis of culture supernatants demonstrated that PelL is an extracellular enzyme, such as the other secondary pectate lyases (17). 

In E. chrysanthemi, the pectate lyase, polygalacturonase and pectin methylesterase activities are induced in the presence of PGA (26, 37). The inducer is not the polymer itself but some breakdown products, initially generated by the... 

As already mentioned before a complete family of pectin lyases is present in A. niger. With all the genes sequenced and individually expressed, sometimes via promoter gene fusions (see below), the way is open to characterize the full spectrum of activities as outlined in the intro-... 

Fig. 1. Schematic overview of Aspergillus niger pectin lyase genes pel A to pelF aa, amino acid m.p. mature protein.

Table 2. Compilation of features and properties of Aspergillus niger pectin lyase genes and enzymes. WT, wild type n.d., not determined.

Expression of pectin lyase genes and localization of corresponding enzymes... 

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