Role of Pectinesterase in pH-Dependent Interactions between Pea Cell Wall Polymers

Extracts of etiolated pea (Pisum sativum L.) shoots converted soluble pectin from the seedlings to a trichloroacetic acid-insoluble form. This activity coincided with pectinesterase peaks separated from the extracts by gel filtration and ion exchange. The conversion of pectin to the trichloroacetic acid-insoluble form and pectinesterase exhibited identical responses to pH, with activity only above pH 6. The formation of trichloroacetic acid-insoluble pectin in pea cell walls and their extracts is due to de-esterification of the pectin by pectinesterase and not to binding between pectin and a protein, as reported in the literature.