Mannan degradation

There is no information so far available about mannan degrading enzymes of alkaliphiles. In this paper, a P-mannan degrading alkaliphile Bacillus sp. AM-001) with high productivities of cell-associated P-mannosidase and three extracellular P-... 

The most characterised D-mannan degrading enzymes are the endo- -mannanases (5). These enzymes act on a range of 1,4-p-D-mannan-type polysaccharides including D-mannan, glucomannans (acetylated and deacetylated), galactomannans and galacto-glucomannans. The extent and... 

Source of D-mannanase References Source of D-mannan° Degradation products... 

L.R.S. Moreira, and E.X.F. Filho, An overview of mannan structure and mannan-degrading... 

The structures of the cell-wall D-mannans of several other yeasts have been investigated381 by use of this exo-a-D-mannanase. Five were degraded to the (l->6)-a-D-mannan chain. Those which contained jB-linked d-mannosyl units or a-D-galactosyl groups in the side chains were not significantly hydrolyzed. However, removal, by partial hydrolysis with acid, of the a-D-galactosyl units from five galactomannans, and of /3-linked D-mannosyl units from three other D-mannans, rendered these polysaccharides partially susceptible to hydrolysis by exo-a-D-mannanase, consistent with an a-linked-D-mannan structure. 

The action of /3-D-mannosidase finally degrades the D-manno-oligo-saccharides, to afford free D-mannose molecules details of this process were given in an earlier article.12 An enzyme identified as oligo-/J-D-mannosyl-(l- 4)-phosphorylase719 may also take part in the mobilization of D-galactomannan in seeds. This enzyme, in the presence of orthophosphate, acts on D-manno-oligosaccharides (obtained from partial hydrolysis of D-mannan), and yields /3-D-mannosyl phosphate. 

Sprucewood holocellulose was treated with an endo-p-1,4-mannanase isolated from Aspergillus niger and an endo-/3-1,4-xylanase, two avicelases, and a cellobiohydrolase C isolated from Trichoderma viride. The mannanase hydrolyzed about a quarter of the mannan in 2-3 days without xylan or cellulose degradation. The xylanase hydrolyzed about half the xylan with 10% mannan solubilization. The three cellulases hydrolyzed up to 45% of the cellulose and 20% of the xylan, accompanied by 40-70% solubilization of the mannan. Combined xylanase-mannanase treatment hydrolyzed about half the xylan and mannan. Addition of mannanase to to cellulose-treated samples increased the degradation of the cellulose and mannan. Micromorphological studies of the variously treated specimens revealed a loss of substances in P/Slf T, and adjacent zones of S2 of the tracheid wall. 

The galactoglucomannan of the holocellulose was degraded by the mannanase. The reaction was slow, but conversion showed a steady increase. After 80 hr of incubation, about 25% of the mannan was transformed into water-soluble products (Table I, Column 10). This figure was calculated on the basis of the mannose, glucose, and galactose present in the acid hydrolysate (cf. Experimental). 

The xylan degradation rates relative to those of mannan ranged from 0.3 to 0.4 at the end of the experiment (80 hr). The same values were obtained before the additional action of mannanase on the samples treated with one of the three cellulases for 48 hr (Table III, Column 14). The corresponding values relative to the cellulose degradation rates ranged from 0.5 to 0.7 for the samples treated with cellulase only (48 hr) and after combined cellulase-mannase action (Table III, Column 15). 

Figure 13. Avicelase 1 + mannan-ase treatment. Degradation of S2 in an earlywood tracheid snowing lamellar aggregation pattern. Scale = 1 fim.

The properties of the enzymes used in this study have been described in former publications (10,11,15). Important for the following interpretation are their hydrolytic specificities. The xylanase did not hydrolyze either isolated mannans or celluloses—or only to a very small extent (10). The same is true for the mannanase with respect to xylans and celluloses (11,15). The avicelases, which were not purified to the same extent as the xylanase and mannanase, did not hydrolyze mannans, but they degraded xylans besides crystalline cellulose (10). Also, the highly purified cellobiohydrolase C (12) degraded xylan to some extent (Dr. E. K. Gum, Jr., personal communication). 

The three cellulases decomposed about 25-45% of the cellulose accompanied by solubilization of about 40-70% of the mannan and, by partial hydrolysis, of about 20% of the xylan present in the untreated sprucewood holocellulose. Based on the degradation products (cf. Table III, Columns 13-15, and Table II), the catalytic actions of the three cellulases—all isolated from Trichoderma viride—are similar or identical. The lower absolute degradation values obtained with cellobiohydrolase C might merely be a result of enzyme concentration. 

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