Has pectate lyase activity. Eliminative cleavage of (1->4)-alpha-D-galacturonan to give oligosaccharides with 4-deoxy-alpha-D-galact-4-enuronosyl groups at their non-reducing ends. Binds 1 Ca(2+) ion. Glycan metabolism; pectin degradation; 2-dehydro-3-deoxy-D-gluconate from pectin: step 2/5. Monomer. Pollen and flowers. The N-terminus is blocked. Causes an allergic reaction in human. This is one of the major allergens of the ragweed pollen. Belongs to the polysaccharide lyase 1 family. Amb a subfamily.