Protopectinase-T: a rhamnogalacturonase able to solubilize protopectin from sugar beet.

Protopectinase-T (PPase-T), isolated from the culture broth of Trametes sanguinea, was able to release pectic substances from sugar beet by degrading rhamnogalacturonan. The smallest polysaccharide (SPS) that can serve as a substrate for PPase-T was prepared from sugar beet pulp by extraction with NaOH and digestion with alpha-L-arabinofuranosidase, alpha-L-arabinase, and beta-(1-->4)-D-galactanase. The reaction products of SPS with PPase-T were isolated by chromatography on DEAE-Toyopearl 650M and Toyopearl HW40-S columns, and analyzed by labeling the reducing ends with [3H]NaBH4 and by 13C NMR spectroscopy. The results indicated that PPase-T cleaved galactopyranosyluronic-rhamnopyranosyl linkages in SPS. Moreover, it was confirmed that the chemical structure of SPS contains a backbone based on units of [-->4)-alpha-D-GalpA-(1-->2)-alpha-L-Rha p-(1-->].