A tale of two pectins: Diverse fine structures can result from identical processive PME treatments on similar high DM substrates

The effects of a processive pectin-methylesterase (PME) treatment on two different pectins, both possessing a high degree of methylesterification (DM), were investigated. While the starting samples were purportedly very similar in fine structure, the intermolecular DM distributions arising from their PME treatments were strikingly different. Herein, a simulation that illuminates the origin of this phenomenon is described. It is concluded that: (1) very different low-DM samples (with the same average DM) can be generated using the same processive PME, simply by a judicious choice of the high DM starting material; (2) observing the intermolecular DM distribution of the products of processive-PME-processing is an extremely sensitive discriminator of the fine structure of high DM starting materials; and (3) for PMEs with unknown action patterns the processive nature of the enzyme is most simply revealed by studying the changes it induces in the intermolecular DM distribution of very-highly-methylesterified homogalacturonans.