Novel Exopolygalacturonases Produced byAlternaria 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 51–80 kDa (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 Kms 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. ma...