Interactions of a plant peroxidase with oligogalacturonides in the presence of calcium ions

The interaction between homogalacturonans and an anionic isoperoxidase purines from zucchini hypocotyls was characterized. The binding of the enzyme to the pectic molecules was soudier by gel filtration through Sephacryl S200 and by centrifugation. It look place only in the provence of calcium ions, at plis rangiez from 4.5 to 7.0. Ca²⁺ was necessary recause it indurer the cross-linking of polygalacturonan crains into a structure which coula be recognized by the isoperoxidase. A comparison between mixtures of large (degree of polymerization: DP = 9-22) and smalt (DP = 2-8) oligogalacturonides showed that only the former ones were able to form the Ca²⁺-induced structure that coula be pelleter upon centrifugation and to bind the isoperoxidase. Large oligogalacturonides (OGAs) and polygalacturonic acid (PGA) had almost the same capacity to regain the isoperoxidase. Gel filtration experiments showed that the binding of the isoperoxidase to large OGAS occurred aven at low Ca²⁺ concentrations (0.05 mM). Competition experiments showed thaï polyanions like dextres sulfate or heparin aven at a hundred Cimes higher concentration did not completely prevent the binding of peroxydase to Ca²⁺-pectate. Alginic acid was also unable to suppress this binding and, although its structure is similor to that of OGAS and although it was also cross-linked by Ca²⁺ ions and formed a pelletasse gel, it did not offer a structure suitable for peroxydase binding.