Abstract

The importance of α -mannosidases in glycoproteins processing and their application in food and pharmaceutical industry led us to further explore plant α -mannosidases. Thus, two α -mannosidases were purified from matured breadfruit (Artocarpus communis) seeds, by successive chromatography on Diethylaminoethyl-Sepharose CL-6B and Sephacryl S-200 HR to apparent homogeneity. The two isoenzymes named Ma and Mb had native molecular weights of approximately 75 and 60 kDa, respectively. Sodium Dodecyl Sulfate- polyacrylamide gel electrophoresis of these α -mannosidases resolved a single protein band with molecular weights estimated to be 75 kDa for isoform Ma and 61 kDa for Mb. Breadfruitα -mannosidases had optima pH (5.6) and temperature (60°C), and appeared to be stable in presence of some detergents such as Hexansulfonic acid sodium salt, Polyoxyethylen-9-lauryl ether, Nonidet P40, Triton X-100 as well as Ca²⁺ and Zn²⁺. The effect of α -mannosidase inhibitors on the two isoenzymes showed that swainsonine and 1,4-dideoxy-1,4-imino mannitol at 0.01 mM totally inhibited their hydrolytic activity, while kifunensine and deoxymannojirimycin at the same concentration had no effect on these enzymes. Substrate specificity tests revealed that the enzymes exerted only α -mannosidase activity and cleaved α -(1,2); α -(1,3) and α -(1,6) linked mannobiose. Since breadfruit seed α -mannosidases were sensitive to furanose transition state analogs such as swainsonine and 1,4-dideoxy-1,4-imino mannitol and showed broad substrate specificity, these enzymes would belong to class II α -mannosidases.

Key words: α -mannosidases, Artocarpus communis, breadfruit, purification, characterization.