NOVEL EXOPOLYGALACTURONASES PRODUCED BY ALTERNARIA-MALI

Three exopolygalacturonases (exoPG) were purified from the culture fil trate of Alternaria mall and characterized. Three exoPGs were distingu ished by chromatographic properties, They contained a large amount of carbohydrates, and the molecular masses were estimated to be 51-80kDa (exoPG I) and 51-58 kDa (exoPG II and III) by SDS-PAGE, After treatmen t with endo-beta-N-acetylglucosaminidase, their molecular masses decre ased equally to 43 kDa, In addition, the amino acid sequences of the N -terminal 20 residues of the three enzymes were identical except for a few amino acid residues, The pH- and thermal stabilities, optimum pHs , and K(m)s for unsatd, oligoGAs among the three exoPGs were very simi lar, However their substrate specificities were clearly different, Exo PG I hydrolyzed satd, oligoGAs faster than 4,5-unsatd. oligoGAs, On th e contrary, exoPG II and III preferred to hydrolyze 4,5-unsatd, oligoG As. No enzyme with a substrate specificity like exoPG II and III has s o far been reported, It was found that A, mall also produced pectate l yase (PL), pectin lyase (PNL), and pectinesterase (PE) but no endoPG u nder these growth conditions.