Carboxylesterase that acts as a key negative regulator of the Wnt signaling pathway by specifically mediating depalmitoleylation of WNT proteins. Serine palmitoleylation of WNT proteins is required for efficient binding to frizzled receptors. [Wnt protein]-O-(9Z)-hexadecenoyl-L-serine + H2O = (9Z)-hexadecenoate + [Wnt protein]-L-serine + H(+) Belongs to the pectinacetylesterase family. Notum subfamily.