Catalyzes the demethylesterification of homogalacturonan components of pectin. May be involved in pollen tube development. [(1->4)-alpha-D-galacturonosyl methyl ester](n) + n H2O = [(1->4)-alpha-D-galacturonosyl](n) + n H(+) + n methanol Optimum pH is 5.5-6.0. Glycan metabolism; pectin degradation; 2-dehydro-3-deoxy-D-gluconate from pectin: step 1/5. Expressed in pollen. Glycosylated. Several isoforms of the allergen exist due to polymorphism. Causes an allergic reaction in human. Allergen from olive pollen. Important in Mediterranean countries and California. Its prevalence is related to the geographic area. Belongs to the pectinesterase family.