Liberates mannose from p-nitrophenyl-alpha-D-mannoside. Hydrolysis of terminal, non-reducing alpha-D-mannose residues in alpha-D-mannosides. Binds 1 zinc ion per subunit. Inhibited by swainsonine but not by 1-desoxymannojirimycin. Optimum pH is 5. Optimum temperature is 65 degrees Celsius. Activity decreases sharply above 70 degrees Celsius. Dimer. Belongs to the glycosyl hydrolase 38 family.