Mannan‐degrading enzymes purified from the crop of the brown garden snail Helix aspersa Müller (Gastropoda Pulmonata)

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Abstract
Two mannan-degrading enzymes were purified from the crop of the terrestrial snail Helix aspersa Müller. The crude extracts were taken from dormant (for 4 months) snails. The enzymes were a βD-mannanase of 37.4 ± 0.3 kDa (EC 3.2.1.78) and a βD-mannosidase of 77.8 ± 1.9 kDa (EC 3.2.1.25). Both enzymes degraded insoluble mannan, releasing either mannose only (β-mannosidase) or oligosaccharides, possibly mannotriose and mannopentaose (β-mannanase). The β-mannanase had a typical endo-activity pattern, while the β-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 β-mannanase also hydrolysed β-linked heteromannans and its affinity for different galactomannans was studied. The Km values, varying from 2.89 ± 0.47 mg × ml–1 to 0.26 ± 0.01 mg × ml–1, revealed the inhibitory effect of the αD-galactosyl residues released. The β-mannosidase was acidic (optimum pH = 3.3) and heat-sensitive (50% residual activity at 42°C after 5 min of pre-incubation), while the β-mannanase remained stable until 48.5°C (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. J. Exp. Zool. 290:125–135, 2001.