Hydrolysis of terminal, non-reducing alpha-D-mannose residues in alpha-D-mannosides. Binds 1 zinc ion per subunit. Tetramer of equimolar amounts of 60 and 58 kDa subunits. A few precursors are secreted. The mature 58 and 60 kDa subunits are lysosomal. Via a protein termed prestarvation factor which is produced and secreted by both growing and developing cells. First cleaved into the mature 58 kDa subunit and an intermediate 82 kDa subunit. The latter is then cleaved to its mature 60 kDa subunit form. These events occur in multiple intracellular compartments. The 60 kDa subunit may form one or more intramolecular disulfide bonds. Belongs to the glycosyl hydrolase 38 family.