Mannan-degrading enzymes purified from the crop of the brown garden snail Helix aspersa Muller (Gastropoda pulmonata)

Two mannan-degrading enzymes were purified from the crop of the terrestrial snail Helix aspersa Muller. The crude extracts were taken from dormant (for 4 months) snails. The enzymes were a betaD-mannanase of 37.4 +/- 0.3 kDa (EC 3.2.1.78) and a betaD-mannosidase of 77.8 +/- 1.9 kDa (EC 3.2.1.25). Both enzymes degraded insoluble mannan, releasing either mannose only (beta -mannosidase) or oligosaccharides, possibly mannotriose and mannopentaose (beta -mannanase). The beta -mannanase had a typical endo-activity pattern, while the beta -mannosidase was an exoenzyme. The incubation of both enzymes with mannan increased the catalysis by 83%. The best synergy was found with 75% mannosidase combined with 25% mannanase. The beta -mannanase also hydrolysed beta -linked heteromannans and its affinity for different galactomannans was studied. The Km values, varying from 2.89 +/- 0.47 mg x ml(-1) to 0.26 +/- 0.01 mg x ml(-1), revealed the inhibitory effect of the alphaD-galactosyl residues released. The beta -mannosidase was acidic (optimum pH = 3.3) and heat-sensitive (50% residual activity at 4.2 degreesC: after 5 min of pre-incubation), while the beta -mannanase remained stable until 48.5 degreesC (50% residual activity) and over a pH range of 4.3-7.5. The properties of these mannanolytic enzymes are discussed in this paper compared with those purified in other gastropods and in a bacterium, Enterococcus casseliflavus, a quite similar strain previously isolated from this snail intestine. The occurrence of thermostable enzymes in H aspersa digestive tract could be a zootechnic parameter of great importance for snail farming. (C) 2001 Wiley-Liss,Inc.