Carboxylesterase that acts as a key negative regulator of the Wnt signaling pathway (PubMed:22669824). Acts by specifically mediating depalmitoleoylation of WNT proteins. Serine palmitoleoylation of WNT proteins is required for efficient binding to frizzled receptors (By similarity). [Wnt protein]-O-(9Z)-hexadecenoyl-L-serine + H2O = (9Z)-hexadecenoate + [Wnt protein]-L-serine + H(+) First appears around the blastoderm margin prior to the onset of gastrulation. In later gastrulation, expressed in the lateral edges and midline of the posterior neural plate. During segmentation, expressed in stripes at the lateral edges and adjacent to the midline of the neural plate, throughout the hindbrain, with strong expression in rhombomeres 3 and 5, and at the midbrain-hindbrain boundary. At 24 hours post-fertilization (hpf), highly expressed in the central nervous system, including the dorsal neural tube and the midbrain-hindbrain boundary. Belongs to the pectinacetylesterase family. Notum subfamily. The molecular function of NOTUM family protein has remained unclear for many years. It was initially thought to hydrolyze glycosaminoglycan (GAG) chains of glypicans, thereby affecting glypicans ability to interact with Wnt ligands. It was later reported to trigger glypican shedding, by mediating cleavage of their GPI-anchor (PubMed:22669824). It was finally shown that it requires glypicans to suppress Wnt signaling, but does not cleave their GPI-anchor. It acts by mediating depalmitoleoylation of WNT proteins, impairing WNT binding to frizzled receptors.