MODE OF ACTION OF RG-HYDROLASE AND RG-LYASE TOWARD RHAMNOGALACTURONANOLIGOMERS - CHARACTERIZATION OF DEGRADATION PRODUCTS USING RG-RHAMNOHYDROLASE AND RG-GALACTURONOHYDROLASE

The mode of action of RG-hydrolase and RG-lyase toward purified linear rhamnogalacturonan (RG) oligomers has been studied. Major tools in th e characterization of the degradation products were the exo-acting RG- rhamnohydrolase and RG-galacturonohydrolase. They were used to prepare a series of standards of RG oligomers for HPAEC. H-1 NMR spectroscopy confirmed the structure assignment made using HPAEC for a selection o f isolated degradation products. Identification of degradation product s from purified RG oligomers was then performed by comparing retention times of HPAEC peaks with those of standards. RG-hydrolase was able t o cleave RG oligomers which contained five Rha units or more, i.e. DP 9 with a Rha unit at both, nonreducing and reducing end. Its preferent ial cleavage site was at four units from the first nonreducing Rha. RG -lyase was active toward oligomers that contained at least six GalA un its, i.e. DP 12 with a GalA at the nonreducing and a Rha at the reduci ng end. The preferential cleavage site was for the smaller oligomers f our residues, and for the largest oligomer six residues from the reduc ing Rha. From the observed cleavage patterns it can be speculated that in hairy regions, the RG stretches have to be at least 13 residues lo ng for RG-hydrolase and 16 residues long for RG-lyase in order to prod uce one tetramer. (C) 1998 Elsevier Science Ltd. All rights reserved.