Alpha-galacturonidase able to catalyze the hydrolysis of the chromogenic substrate p-nitrophenyl-alpha-D-galacturonic acid (pNPalphaGalUA). It is probable that alpha-1,4-di-galacturonate (GalUA(2)) is the naturally occurring substrate. [(1->4)-alpha-D-galacturonosyl](n) + H2O = [(1->4)-alpha-D-galacturonosyl](n-1) + alpha-D-galacturonate Binds 1 Mn(2+) ion per subunit. Homotetramer. Belongs to the glycosyl hydrolase 4 family.