Anti-MAST antibodies enable researchers to detect and measure the MAST antigen in biological samples. This target is a reported synonym of the SPACA9 gene, which encodes sperm acrosome associated 9. This protein is a known microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) of multiciliated respiratory cells and the distal singlet microtubules of monoflagellated spermatozoa. The human version of MAST has a canonical amino acid length of 222 residues and a protein mass of 25.2 kilodaltons, although 2 isoforms have been identified. It is reported to be localized in the nucleus, cytoplasmic vesicles, and cytoplasm of cells and notably expressed in the testis, nasopharynx, fallopian tube, endometrium, and bronchus.