PEL activity of Ptxt PL1-27 expressed in Escherichia coli . PEL activity was measured as the formation of unsaturated uronides. Effect of pH (A) and Ca2+ ions (B). Means of five replicates ± standard error. Vector denotes the proteins extracted from the bacteria expressing the vector without Ptxt PL1-27. EDTA, ethylenediaminetetraacetic acid.