Novel Exopolygalacturonases Produced by Alternaria mali

Abstract

Three exopolygalacturonases (exoPG) were purified from the culture filtrate of Alternaria mali and characterized; Three exoPGs were distinguished 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 treatment with endo-β-N-acetylglucosaminidase, their molecular masses decreased 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_ms for unsatd. oligoGAs among the three exoPGs were very similar. However their substrate specificities were clearly different. ExoPG I hydrolyzed satd. oligoGAs faster than 4, 5-unsatd. oligoGAs. On the contrary, exoPG II and III preferred to hydrolyze 4, 5-unsatd. oligoGAs. No enzyme with a substrate specificity like exoPG II and III has so far been reported. It was found that A. mali also produced pectate lyase (PL), pectin lyase (PNL), and pectinesterase (PE) but no endoPG under these growth conditions.