Liberates mannose from p-nitrophenyl-alpha-D-mannoside (PubMed:12325362, PubMed:4973951, PubMed:1156387). Liberates mannose from further alpha-D-mannosides including methyl-, benzyl-alpha-D-mannoside, 1-6-linked di-, tri- and tetrasaccharides of alpha-D-mannose and mannosyl-rhamnose (PubMed:12325362). Liberates mannose from various glycoproteins like ovalbumin and ovomucoid (PubMed:12325362, PubMed:5145). Does not hydrolyze beta-D-mannosides (PubMed:12325362). Has glycosyltransferase activity, forming disaccharides from mannose and lyxose but not from glucose, galactose, ribose, xylose or arabinose (PubMed:12325362). Hydrolysis of terminal, non-reducing alpha-D-mannose residues in alpha-D-mannosides. Binds 1 zinc ion per subunit. Inhibited by 2,3,4,6-tetra-O-acetyl-5-fluoro-beta-L-gulopyranosyl fluoride which acts as a slow substrate, doubling as a competitive inhibitor as it forms a high steady state concentration of glycosyl-enzyme intermediate that blocks the active site (PubMed:9442045). Inhibited by 2,3,4,6-tetra-O-acetyl-5-fluoro-alpha-D-mannopyranosyl fluoride which also acts as a slow substrate but no intermediates accumulate (PubMed:9442045). Inhibited by EDTA (PubMed:4973951, PubMed:1156387, PubMed:21924285). Inhibited by metal ion Cu(2+) (PubMed:4973951, PubMed:1156387). Inhibited by metal ions Fe(2+), Cd(2+) and Co(2+) (PubMed:4973951). Inhibited by metal ions Ag(+) and Hg(2+) (PubMed:12325362, PubMed:4973951). Competitively inhibited by mannono-1-4-lactone and mannono-1-5-lactone (PubMed:12325362). Inhibited by swainsonine but not by 1-desoxymannojirimycin (PubMed:21924285). Inhibited by pyrrolidine-3,4-diol derivatives (PubMed:15974577). Optimum pH is 4-5 (PubMed:12325362, PubMed:5145, PubMed:21924285). Activity is stable between pH 4.0 and pH 7.0 in the presence of Zn(2+) (PubMed:4973951). Activity is stable between pH 6.0 and pH 8.5, decreases below pH 5.5 at 25 degrees Celsius (PubMed:12325362). Activity is lost at pH 3 and lower, rapidly diminishes at pH 7-10 but is higher and longest at pH 11-12 (PubMed:21924285). Retains 50% activity after 5 min at 70 degrees Celsius (PubMed:12325362). Retains full activity after 5 min at 70 degrees Celsius but is completely inactive after 5 min at 80 degrees Celsius (PubMed:5145). Retains 100%, 50% and <10% activity after 2 hours at 40, 55 and 70 degrees Celsius, respectively (PubMed:21924285). Dimer of dimers of heavy and light subunits. Expressed from very early on in developing cotyledons. Produced as a precursor which is then proteolytically cleaved into a 66kD heavy subunit and a 44kD light subunit. Cleavage probably occurs in protein bodies/protein storage vacuoles. Belongs to the glycosyl hydrolase 38 family.