Acts in the modification of cell walls via demethylesterification of cell wall pectin. [(1->4)-alpha-D-galacturonosyl methyl ester](n) + n H2O = [(1->4)-alpha-D-galacturonosyl](n) + n H(+) + n methanol Glycan metabolism; pectin degradation; 2-dehydro-3-deoxy-D-gluconate from pectin: step 1/5. In the peel, expression is localized to the region of the flavedo close to the oil glands, and to the innermost layer of the albedo. In the lamella, expression is localized to the cell layers opposing the fruit tissue, and to the parenchyma surrounding the vascular tissue. In the fruit vesicles, expression is restricted to the peripheral cell layers and stalk cells. High levels of expression are detected in the core matrix. The PMEI region may act as an autoinhibitory domain and prevent untimely PME activity during transport. In the N-terminal section; belongs to the PMEI family. In the C-terminal section; belongs to the pectinesterase family.