Enzymatic degradation of amylouronate (α-(1 → 4)-linked glucuronan) by α-glucuronidase from Paenibacillus sp. TH501b

Enzymatic degradation of amylouronate (α-(1 → 4)-linked polyglucuronic acid sodium salt, α-(1 → 4)-linked glucuronan), which was prepared from water-soluble starch by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation, was investigated. A bacterial strain TH501b capable of degrading amylouronate was isolated from soil samples collected in the natural environment. Molecular analysis of the 16S rRNA gene showed that TH501b belongs to the genus Paenibacillus. A hydrolytic enzyme responsible for the degradation of amylouronate, amylouronate hydrolase-I (AUH-I), was detected in the cell-free extract of TH501b. AUH-I was purified by four steps of column chromatography and some properties were characterized. The molecular mass of the native AUH-I was estimated to be approximately 115 kDa by size exclusion chromatography (SEC), whereas sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed two major bands at 80 kDa and 46 kDa, respectively. The enzyme was most active at pH 6.0-7.0 and 30 °C. The SEC analysis of reaction products revealed that AUH-I liberated glucuronate as a sole product from amylouronate, indicating that AUH-I hydrolyzed amylouronate exolytically, and thus, was classified as α-glucuronidase.