Mechanism of action of D-galacturonan digalacturonohydrolase of Selenomonas ruminantium on oligogalactosiduronic acids.
The mechanism of action of the specific D-galacturonan digalacturonohydrolase [poly-(1----4)-alpha-D-galactosiduronate digalacturonohydrolase, EC 3.2.1.82] of Selenomonas ruminantium was investigated by using reducing-end [1-3H]-labeled oligogalactosiduronates having degree of polymerization 3-5 as the substrates. The reaction products, incorporation and distribution of radioactivity in products, and the frequency of oligogalactosiduronate bond-cleavage were quantitatively estimated as functions of the substrate concentration. An alternative cleavage of tri(D-galactosiduronate) occurred during the enzyme reaction, indicating the participation of some bimolecular mechanism in addition to unimolecular hydrolysis in the action of the enzyme. Unimolecular hydrolysis takes place at low initial concentration of the substrate. The shifted termolecular enzyme-substrate complex formation and the subsequent galactosyluronic transfer is the predominant mechanism in degradation of tri(D-galactosiduronate) at high concentration. Tetra(D-galactosiduronate) and penta(D-galactosiduronate) are degraded by unimolecular hydrolysis at low, as well as high concentration of the substrate.
Heinrichová
K
K
Institute of Chemistry, Slovak Academy of Sciences, Czechoslovakia.
Dzúrová
M
M
Rexová-Benková
L
L
D001438:Bacteroidaceae / Q000201:enzymology*; D002240:Carbohydrate Sequence; D006026:Glycoside Hydrolases / Q000378:metabolism*; D006031:Glycosylation; D007700:Kinetics; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000378:metabolism*; D013379:Substrate Specificity; D014316:Tritium
D009844:Oligosaccharides; D014316:Tritium; D006026:Glycoside Hydrolases; C065616:exo-poly-alpha-galacturonosidase