Pectinesterase

Pectinesterase, or pectin methylesterase (PME), is a plant cell-wall–associated enzyme that removes methyl ester groups from pectin, a key polysaccharide in plant cell walls. It catalyzes the hydrolysis of methyl esters on the homogalacturonan backbone, releasing methanol and creating free carboxylate groups on galacturonic acid residues.

Substrate and pattern: Pectin is typically found as homogalacturonan with varying degrees of methylation. PME action reduces esterification, and the resulting demethylated regions can form calcium cross-links or become targets for polygalacturonases, depending on the pattern of demethylation (blockwise or random).

Biological roles: PME is widespread in plants and is secreted into the apoplast. It participates in cell-wall remodeling during growth, fruit ripening, abscission, and pollen tube guidance. Its activity often collaborates with polygalacturonases to promote softening and tissue loosening.

Regulation and diversity: PME activity is pH-dependent and modulated by Ca2+ ions. Plants also produce pectin methylesterase inhibitors (PMEIs) that restrain PME activity; multiple isoforms exhibit different substrate preferences and tissue distributions.

Industrial relevance: In food processing, PME is used to adjust pectin gelation, viscosity, and juice-cloud stability. It can influence texture in fruit products and affect clarification and recovery in juice and wine production.