Erwinia exopolygalacturonate lyase is strongly activated by Na+, but very weakly by divalent cations such as Ca2+, in contrast to most of the knownpectic lyases; nevertheless, this enzyme is completely inhibited by 1 mM EDTA. In this work, six polyamino carboxylates such as EDTA and a polyamine were examined for their effects on the enzyme activity. EDTA, trans-1, 2-cyclohexanediaminetetraacetate, and diethylenetriaminepentaacetate inhibited the enzyme stron ly, but ethylenediaminediacetate showed little inhibition. Only triethylenetetramine stimulated the enzyme. The removal of EDTA from the enzyme solution resulted in an almost complete restoration of the activity. The EDTA-treated enzyme as well as the untreated one revealed no requirement for any divalent cations. The inactivation by hydroxyethylenediaminetriacetate, a mild inhibitor, was the mixed type. It seems most likely that the inactivation by the polyamino carboxylates is caused not by sequestering any metals but by directly forming an enzyme-chelator complex.
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Ikeda et al. (1984) studied this question.