The degradation of oligogalacturonides by the polygalacturonase of Bacillus polymyxa

Studies were made of the action of the polygalacturonase of Bacillus polymyxa (BPG) on the lower Oligogalacturonides. Both the crude exocellular enzyme and fractions separated by cellulose chromatography were able to hydrolyze trigalacturonic acid but not digalacturonic acid. Hydrolysis of trigalacturonate by BPG yields the altered dimer and monogalacturonate, while hydrolysis of the tetramer yields monomer and an altered trimer and, at a slower rate, normal dimer and an altered dimer. In addition, evidence is presented that the polygalacturonase attacks from the non-reducing end. One of the major end products of the action of BPG on pectic substances appears to be a dimer which is different from normal digalacturonate. This compound has been purified and partially characterized. The carboxyl to aldehyde group ratio is 1.98. Assuming one aldehyde group per molecule, the calculated molecular weight of the free acid is almost identical with that of normal dimer (367 and 370, respectively). The specific rotation [α]_D²² of the altered dimer is +177.8 ° (which is similar to that of normal dimer [α]_D²² = +173 °). This suggests that the altered dimer has retained the α configuration. This compound shows a strong absorption peak between 230 and 235 mμ which in turn indicates that it contains an α,β unsaturated bond. Thus, it was concluded that the enzyme is actually a trans-eliminase rather than a hydrolase. The altered dimer is not hydrolyzed by BPG. However, both this compound and normal dimer are attacked by a digalacturonicidase contained within the cells.