摘要：

An extracellular alpha-mannosidase with unusual properties was purified from the digestive fluid of oil palm weevil (Rhynchophorus palmarum Linnaeus) larvae using ammonium sulphate saturation, size exclusion and anion-exchange chromatography. The enzyme named RpltM is thermoacidophilic, thermostable and behaves like lysosomal alpha-mannosidase (EC 3.2.1.24). The molecular weight, K-m value, optimum reaction temperature and pH are 108-112 kDa, 0.36 mM, 65 degrees C and 4.5, respectively. Zn2+ enhanced whereas Cu2+ Sodium dodecyl sulphate, swainsonine and 1,4-dideoxy-1,4-iminomannitol strongly inhibited its hydrolytic activity. The enzyme was stable for 25 min at 65 degrees C and retained 70% of its initial activity after 60 min. At 70 degrees C, around 60% of this activity was conserved after 25 min. RpltM retained more than 90% of its activity over a pH range of 4.2 to 5.0 and remained fully active in the presence of detergents such as nonidet P-40, triton X-100, polyoxyethylen-10-oleyl ether (up to 1%, w/v), dithiothreitol and beta-mercaptoethanol. The stability under these conditions is also better than that reported for other insect alpha-mannosidases. Thus, RpltM could be used as an important bioindustrial tool for removing mannose residues from oligosaccharides.

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