Degradation pullulan

Poly(L-malate) [poly(malic acid) (PMA)], is a water-soluble polyanion produced by slime molds and some yeasts such as Physarum polycephalum or Aureobasidium pullulans, respectively. Its function and metabolism has been studied during the last few years [122-125]. Recently, several PMA-degrad-ing bacteria have been isolated, and a cytoplasmic membrane-bound PMA hydrolase was purified from Comamonas acidovans strain 7789 [126] that... 

Table L Action of Pullulan Degrading Enzymes on Pullulan and Starch...

FIGURE 2 Degradation of pullulan (MW 200,000) in replicate anaerobic enrichment cultures of marine bacteria from anoxic sediments. Open circles show total pullulan concentrations remaining in the medium at each time point. The molecular weight distribution of the pullulan is shown by the stacked bars white >10,000 Da, stripes 5000 Da, black <1200 Da. Note that the lower molecular weight fraction progressively accumulated between 50 and 64 h. [Data from Arnosti et al. (1994).]... 

The plant and bacterial enzymes capable of hydrolyzing pullulan do not have identical specificities. In particular, the plant enzymes have little or no action on glycogen and phytoglycogen under conditions in which they readily hydrolyze amylopectin and its /3-dextrin. To stress this difference (the bacterial enzymes are capable of degrading both glycogen and phytoglycogen), Manners (1997) recommended different nomenclature for bacterial enzymes, to be called pullulanase, and the plant enzymes, to be called limit dextrinases. 

Pullulanase type I hydrolyzes a-1,6 linkages in amylopectin, pullulan or limit dextrins with high specificity. Pullulan is completely degraded in a random fashion... 

Information on the hydrolytic activity in marine sediments has been obtained from the use of model substrates labeled with fluorescent dyes such as methylumbelliferone (MUF) or fluorescein. These substrates may be small dimeric molecules, the hydrolytic cleavage of which releases the fluorescence signal, which is then indicative of the activity of specific enzymes such as glucosidase, chitobiase, lipase, ami-nopeptidase or esterase (Chrost 1991). Also large fluorescently labeled polymers such as the polysaccharides laminarin or pullulan have been used in experiments to demonstrate the mechanism and kinetics of bacterial degradation (Amosti 1996). 

This is only the case if pullulan is treated (by mild treatment with acid or by boiling) to inactivate an associated a-n-glucosidase if this is not done, further degradation of the maltotriose occurs. 

Some polysaccharides, like pullulan, can be precipitated selectively in plates with ethanol (8). Polyanionic polysaccharides like pectin or carboxy methyl cellulose (CMC) can be precipitated with cetylammonium salts (9, 10). Degradation zones in these plates will not turn opaque upon addition of the precipitant thus revealing the activity of polysaccharases. 

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