Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The mode of action of the isolated form of tomato endo-D-galacturonanase of molecular weight close to 50 000 was investigated with oligo-D-galactosiduronic acids of polymerization degree 2-7 and their derivatives the terminal aldehyde group of which was reduced. The rate of hydrolysis, catalysed by this enzyme decreased with the shortening the chain length of oligo-D-galactosiduronates used; di(D-galactosiduronic) acid was not hydrolyzed by this enzyme at all. Tri(D-galactosiduronic) acid was cleaved into monomer and dimer, tetra(D-galactosiduronic) acid was alternatively cleaved into monomer and trimer, as well as into two dimers. The previously proposed conception that the binding site of the tomato endo-D-galacturonanase contains three subsites and that the catalytic groups are localized close to the first bond from the reducing end of the substrate segment bound in the complex were proved. The mode of hydrolysis of the reduced oligomers is in favour of the mentioned conception.