alpha-Mannosidase (EC 3.2.1.24, alpha-D-mannosidase, p-nitrophenyl-alpha-mannosidase, alpha-D-mannopyranosidase, 1,2-alpha-mannosidase, 1,2-alpha-D-mannosidase, exo-alpha-mannosidase) is an enzyme involved in the cleavage of the alpha form of mannose. Its systematic name is alpha-D-mannoside mannohydrolase. Humans express the following three alpha-mannosidase isozymes: It can be utilized in experiments that determine the effects of the presence or absence of mannose on specific molecules, such as recombinant proteins that are used in vaccine development. A deficiency can lead to alpha-mannosidosis.