Sialic acids are acidic 9-carbon sugars typically found at the non-reducing end of sugar chains. They are frequently modified by 9-O-acetylation and this modification is removed by sialic acid acetylesterases. SIAE catalyzes the removal of O-acetyl ester groups from position 9 of the parent sialic acid, N-acetylneuraminic acid. SIAE appears to encode both lysosomal and cytosolic sialic acid acetylesterase isoforms (LSE and CSE, respectively). It is widely expressed with high expression in the testis, prostate, and colon. There are three named isoforms.